diff --git a/src/Analyser/MutatingScope.php b/src/Analyser/MutatingScope.php
index bbd489a844..1149594fcd 100644
--- a/src/Analyser/MutatingScope.php
+++ b/src/Analyser/MutatingScope.php
@@ -1400,6 +1400,11 @@ private function resolveType(Expr $node): Type
 				return new ErrorType();
 			}
 
+			if (($leftType->isString()->yes() && !$leftType->isNumericString()->yes())
+				|| ($rightType->isString()->yes() && !$rightType->isNumericString()->yes())) {
+				return new ErrorType();
+			}
+
 			$leftNumberType = $leftType->toNumber();
 			$rightNumberType = $rightType->toNumber();
 
diff --git a/src/Type/Accessory/AccessoryLiteralStringType.php b/src/Type/Accessory/AccessoryLiteralStringType.php
index a271bb2a07..ad874199e6 100644
--- a/src/Type/Accessory/AccessoryLiteralStringType.php
+++ b/src/Type/Accessory/AccessoryLiteralStringType.php
@@ -164,6 +164,11 @@ public function toArray(): Type
 		);
 	}
 
+	public function isString(): TrinaryLogic
+	{
+		return TrinaryLogic::createYes();
+	}
+
 	public function isNumericString(): TrinaryLogic
 	{
 		return TrinaryLogic::createMaybe();
diff --git a/src/Type/Accessory/AccessoryNonEmptyStringType.php b/src/Type/Accessory/AccessoryNonEmptyStringType.php
index b8f50792e1..048a1d946e 100644
--- a/src/Type/Accessory/AccessoryNonEmptyStringType.php
+++ b/src/Type/Accessory/AccessoryNonEmptyStringType.php
@@ -160,6 +160,11 @@ public function toArray(): Type
 		);
 	}
 
+	public function isString(): TrinaryLogic
+	{
+		return TrinaryLogic::createYes();
+	}
+
 	public function isNumericString(): TrinaryLogic
 	{
 		return TrinaryLogic::createMaybe();
diff --git a/src/Type/Accessory/AccessoryNumericStringType.php b/src/Type/Accessory/AccessoryNumericStringType.php
index 75d044bb7e..1a2123b833 100644
--- a/src/Type/Accessory/AccessoryNumericStringType.php
+++ b/src/Type/Accessory/AccessoryNumericStringType.php
@@ -156,6 +156,11 @@ public function toArray(): Type
 		);
 	}
 
+	public function isString(): TrinaryLogic
+	{
+		return TrinaryLogic::createYes();
+	}
+
 	public function isNumericString(): TrinaryLogic
 	{
 		return TrinaryLogic::createYes();
diff --git a/src/Type/Accessory/HasOffsetType.php b/src/Type/Accessory/HasOffsetType.php
index edf56ef6b0..5804ded061 100644
--- a/src/Type/Accessory/HasOffsetType.php
+++ b/src/Type/Accessory/HasOffsetType.php
@@ -134,6 +134,11 @@ public function isArray(): TrinaryLogic
 		return TrinaryLogic::createMaybe();
 	}
 
+	public function isString(): TrinaryLogic
+	{
+		return TrinaryLogic::createMaybe();
+	}
+
 	public function isNumericString(): TrinaryLogic
 	{
 		return TrinaryLogic::createMaybe();
diff --git a/src/Type/Accessory/NonEmptyArrayType.php b/src/Type/Accessory/NonEmptyArrayType.php
index 57094d492f..9c4419d69b 100644
--- a/src/Type/Accessory/NonEmptyArrayType.php
+++ b/src/Type/Accessory/NonEmptyArrayType.php
@@ -139,6 +139,11 @@ public function isArray(): TrinaryLogic
 		return TrinaryLogic::createYes();
 	}
 
+	public function isString(): TrinaryLogic
+	{
+		return TrinaryLogic::createNo();
+	}
+
 	public function isNumericString(): TrinaryLogic
 	{
 		return TrinaryLogic::createNo();
diff --git a/src/Type/ArrayType.php b/src/Type/ArrayType.php
index cf6dda2f9f..82272a1a3e 100644
--- a/src/Type/ArrayType.php
+++ b/src/Type/ArrayType.php
@@ -199,6 +199,11 @@ public function isArray(): TrinaryLogic
 		return TrinaryLogic::createYes();
 	}
 
+	public function isString(): TrinaryLogic
+	{
+		return TrinaryLogic::createNo();
+	}
+
 	public function isNumericString(): TrinaryLogic
 	{
 		return TrinaryLogic::createNo();
diff --git a/src/Type/CallableType.php b/src/Type/CallableType.php
index 5b96b285bc..d13f571e2e 100644
--- a/src/Type/CallableType.php
+++ b/src/Type/CallableType.php
@@ -304,6 +304,11 @@ public function isArray(): TrinaryLogic
 		return TrinaryLogic::createMaybe();
 	}
 
+	public function isString(): TrinaryLogic
+	{
+		return TrinaryLogic::createMaybe();
+	}
+
 	public function isNumericString(): TrinaryLogic
 	{
 		return TrinaryLogic::createNo();
diff --git a/src/Type/ClassStringType.php b/src/Type/ClassStringType.php
index aa79e138dd..f37d5d3ff2 100644
--- a/src/Type/ClassStringType.php
+++ b/src/Type/ClassStringType.php
@@ -62,6 +62,11 @@ public function isSuperTypeOf(Type $type): TrinaryLogic
 		return TrinaryLogic::createNo();
 	}
 
+	public function isString(): TrinaryLogic
+	{
+		return TrinaryLogic::createYes();
+	}
+
 	public function isNumericString(): TrinaryLogic
 	{
 		return TrinaryLogic::createMaybe();
diff --git a/src/Type/ClosureType.php b/src/Type/ClosureType.php
index f2ccf89e93..ed82d34117 100644
--- a/src/Type/ClosureType.php
+++ b/src/Type/ClosureType.php
@@ -381,6 +381,11 @@ public function isArray(): TrinaryLogic
 		return TrinaryLogic::createNo();
 	}
 
+	public function isString(): TrinaryLogic
+	{
+		return TrinaryLogic::createNo();
+	}
+
 	public function isNumericString(): TrinaryLogic
 	{
 		return TrinaryLogic::createNo();
diff --git a/src/Type/Constant/ConstantStringType.php b/src/Type/Constant/ConstantStringType.php
index 8fdab07c8d..1407a7f66e 100644
--- a/src/Type/Constant/ConstantStringType.php
+++ b/src/Type/Constant/ConstantStringType.php
@@ -240,6 +240,11 @@ public function toFloat(): Type
 		return new ConstantFloatType((float) $this->value);
 	}
 
+	public function isString(): TrinaryLogic
+	{
+		return TrinaryLogic::createYes();
+	}
+
 	public function isNumericString(): TrinaryLogic
 	{
 		return TrinaryLogic::createFromBoolean(is_numeric($this->getValue()));
diff --git a/src/Type/FloatType.php b/src/Type/FloatType.php
index 9b14721832..790752ed57 100644
--- a/src/Type/FloatType.php
+++ b/src/Type/FloatType.php
@@ -118,6 +118,11 @@ public function isArray(): TrinaryLogic
 		return TrinaryLogic::createNo();
 	}
 
+	public function isString(): TrinaryLogic
+	{
+		return TrinaryLogic::createNo();
+	}
+
 	public function isNumericString(): TrinaryLogic
 	{
 		return TrinaryLogic::createNo();
diff --git a/src/Type/IntersectionType.php b/src/Type/IntersectionType.php
index 87c80d8b6f..90144aa5e1 100644
--- a/src/Type/IntersectionType.php
+++ b/src/Type/IntersectionType.php
@@ -349,6 +349,11 @@ public function isArray(): TrinaryLogic
 		return $this->intersectResults(static fn (Type $type): TrinaryLogic => $type->isArray());
 	}
 
+	public function isString(): TrinaryLogic
+	{
+		return $this->intersectResults(static fn (Type $type): TrinaryLogic => $type->isString());
+	}
+
 	public function isNumericString(): TrinaryLogic
 	{
 		return $this->intersectResults(static fn (Type $type): TrinaryLogic => $type->isNumericString());
diff --git a/src/Type/IterableType.php b/src/Type/IterableType.php
index 8eeb62d74a..a9e4c7e0d1 100644
--- a/src/Type/IterableType.php
+++ b/src/Type/IterableType.php
@@ -228,6 +228,11 @@ public function isArray(): TrinaryLogic
 		return TrinaryLogic::createMaybe();
 	}
 
+	public function isString(): TrinaryLogic
+	{
+		return TrinaryLogic::createNo();
+	}
+
 	public function isNumericString(): TrinaryLogic
 	{
 		return TrinaryLogic::createNo();
diff --git a/src/Type/JustNullableTypeTrait.php b/src/Type/JustNullableTypeTrait.php
index f3f2847495..e1c10120b1 100644
--- a/src/Type/JustNullableTypeTrait.php
+++ b/src/Type/JustNullableTypeTrait.php
@@ -58,6 +58,11 @@ public function isArray(): TrinaryLogic
 		return TrinaryLogic::createNo();
 	}
 
+	public function isString(): TrinaryLogic
+	{
+		return TrinaryLogic::createNo();
+	}
+
 	public function isNumericString(): TrinaryLogic
 	{
 		return TrinaryLogic::createNo();
diff --git a/src/Type/MixedType.php b/src/Type/MixedType.php
index 7c130546a3..1213e3fc42 100644
--- a/src/Type/MixedType.php
+++ b/src/Type/MixedType.php
@@ -405,6 +405,11 @@ public function isArray(): TrinaryLogic
 		return TrinaryLogic::createMaybe();
 	}
 
+	public function isString(): TrinaryLogic
+	{
+		return TrinaryLogic::createMaybe();
+	}
+
 	public function isNumericString(): TrinaryLogic
 	{
 		return TrinaryLogic::createMaybe();
diff --git a/src/Type/NeverType.php b/src/Type/NeverType.php
index 0fa866a387..440de1a262 100644
--- a/src/Type/NeverType.php
+++ b/src/Type/NeverType.php
@@ -231,6 +231,11 @@ public function isArray(): TrinaryLogic
 		return TrinaryLogic::createNo();
 	}
 
+	public function isString(): TrinaryLogic
+	{
+		return TrinaryLogic::createNo();
+	}
+
 	public function isNumericString(): TrinaryLogic
 	{
 		return TrinaryLogic::createNo();
diff --git a/src/Type/NullType.php b/src/Type/NullType.php
index 29f15f0b20..f86b990074 100644
--- a/src/Type/NullType.php
+++ b/src/Type/NullType.php
@@ -175,6 +175,11 @@ public function isArray(): TrinaryLogic
 		return TrinaryLogic::createNo();
 	}
 
+	public function isString(): TrinaryLogic
+	{
+		return TrinaryLogic::createNo();
+	}
+
 	public function isNumericString(): TrinaryLogic
 	{
 		return TrinaryLogic::createNo();
diff --git a/src/Type/ObjectType.php b/src/Type/ObjectType.php
index a615e24977..671bb56205 100644
--- a/src/Type/ObjectType.php
+++ b/src/Type/ObjectType.php
@@ -779,6 +779,11 @@ public function isArray(): TrinaryLogic
 		return TrinaryLogic::createNo();
 	}
 
+	public function isString(): TrinaryLogic
+	{
+		return TrinaryLogic::createNo();
+	}
+
 	public function isNumericString(): TrinaryLogic
 	{
 		return TrinaryLogic::createNo();
diff --git a/src/Type/StaticType.php b/src/Type/StaticType.php
index 6d681bd720..18599c356e 100644
--- a/src/Type/StaticType.php
+++ b/src/Type/StaticType.php
@@ -332,6 +332,11 @@ public function isArray(): TrinaryLogic
 		return $this->getStaticObjectType()->isArray();
 	}
 
+	public function isString(): TrinaryLogic
+	{
+		return $this->getStaticObjectType()->isString();
+	}
+
 	public function isNumericString(): TrinaryLogic
 	{
 		return $this->getStaticObjectType()->isNumericString();
diff --git a/src/Type/StrictMixedType.php b/src/Type/StrictMixedType.php
index f98580057f..09e00d0bd0 100644
--- a/src/Type/StrictMixedType.php
+++ b/src/Type/StrictMixedType.php
@@ -151,6 +151,11 @@ public function isArray(): TrinaryLogic
 		return TrinaryLogic::createNo();
 	}
 
+	public function isString(): TrinaryLogic
+	{
+		return TrinaryLogic::createNo();
+	}
+
 	public function isNumericString(): TrinaryLogic
 	{
 		return TrinaryLogic::createNo();
diff --git a/src/Type/StringType.php b/src/Type/StringType.php
index cf47790a72..8abcad2769 100644
--- a/src/Type/StringType.php
+++ b/src/Type/StringType.php
@@ -133,6 +133,11 @@ public function toArray(): Type
 		);
 	}
 
+	public function isString(): TrinaryLogic
+	{
+		return TrinaryLogic::createYes();
+	}
+
 	public function isNumericString(): TrinaryLogic
 	{
 		return TrinaryLogic::createMaybe();
diff --git a/src/Type/Traits/ObjectTypeTrait.php b/src/Type/Traits/ObjectTypeTrait.php
index 40f6ef6a60..be20a00f5e 100644
--- a/src/Type/Traits/ObjectTypeTrait.php
+++ b/src/Type/Traits/ObjectTypeTrait.php
@@ -105,6 +105,11 @@ public function isArray(): TrinaryLogic
 		return TrinaryLogic::createNo();
 	}
 
+	public function isString(): TrinaryLogic
+	{
+		return TrinaryLogic::createNo();
+	}
+
 	public function isNumericString(): TrinaryLogic
 	{
 		return TrinaryLogic::createNo();
diff --git a/src/Type/Type.php b/src/Type/Type.php
index 24a17d63c5..5c0b727d7c 100644
--- a/src/Type/Type.php
+++ b/src/Type/Type.php
@@ -98,6 +98,8 @@ public function isSmallerThan(Type $otherType): TrinaryLogic;
 
 	public function isSmallerThanOrEqual(Type $otherType): TrinaryLogic;
 
+	public function isString(): TrinaryLogic;
+
 	public function isNumericString(): TrinaryLogic;
 
 	public function isNonEmptyString(): TrinaryLogic;
diff --git a/src/Type/UnionType.php b/src/Type/UnionType.php
index d7cd5380ae..b3a95c4231 100644
--- a/src/Type/UnionType.php
+++ b/src/Type/UnionType.php
@@ -391,6 +391,11 @@ public function isArray(): TrinaryLogic
 		return $this->unionResults(static fn (Type $type): TrinaryLogic => $type->isArray());
 	}
 
+	public function isString(): TrinaryLogic
+	{
+		return $this->unionResults(static fn (Type $type): TrinaryLogic => $type->isString());
+	}
+
 	public function isNumericString(): TrinaryLogic
 	{
 		return $this->unionResults(static fn (Type $type): TrinaryLogic => $type->isNumericString());
diff --git a/src/Type/VoidType.php b/src/Type/VoidType.php
index 0c40218abe..166ca12ee4 100644
--- a/src/Type/VoidType.php
+++ b/src/Type/VoidType.php
@@ -100,6 +100,11 @@ public function isArray(): TrinaryLogic
 		return TrinaryLogic::createNo();
 	}
 
+	public function isString(): TrinaryLogic
+	{
+		return TrinaryLogic::createNo();
+	}
+
 	public function isNumericString(): TrinaryLogic
 	{
 		return TrinaryLogic::createNo();
diff --git a/tests/PHPStan/Analyser/NodeScopeResolverTest.php b/tests/PHPStan/Analyser/NodeScopeResolverTest.php
index 088619e961..3535aac6dc 100644
--- a/tests/PHPStan/Analyser/NodeScopeResolverTest.php
+++ b/tests/PHPStan/Analyser/NodeScopeResolverTest.php
@@ -704,6 +704,7 @@ public function dataFileAsserts(): iterable
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-6500.php');
 
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-6488.php');
+		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-6624.php');
 	}
 
 	/**
diff --git a/tests/PHPStan/Analyser/data/bug-6624.php b/tests/PHPStan/Analyser/data/bug-6624.php
new file mode 100644
index 0000000000..bbdf3b9395
--- /dev/null
+++ b/tests/PHPStan/Analyser/data/bug-6624.php
@@ -0,0 +1,31 @@
+<?php
+
+namespace Bug6624;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @param non-empty-string $foo
+ * @param string $bar
+ */
+function bug6624_should_error($foo, $bar) {
+	assertType('*ERROR*',$foo + 10);
+	assertType('*ERROR*',$foo - 10);
+	assertType('*ERROR*',$foo * 10);
+	assertType('*ERROR*',$foo / 10);
+
+	assertType('*ERROR*',10 + $foo);
+	assertType('*ERROR*',10 - $foo);
+	assertType('*ERROR*',10 * $foo);
+	assertType('*ERROR*',10 / $foo);
+
+	assertType('*ERROR*',$bar + 10);
+	assertType('*ERROR*',$bar - 10);
+	assertType('*ERROR*',$bar * 10);
+	assertType('*ERROR*',$bar / 10);
+
+	assertType('*ERROR*',10 + $bar);
+	assertType('*ERROR*',10 - $bar);
+	assertType('*ERROR*',10 * $bar);
+	assertType('*ERROR*',10 / $bar);
+}
diff --git a/tests/PHPStan/Rules/Api/data/class-implements-out-of-phpstan.php b/tests/PHPStan/Rules/Api/data/class-implements-out-of-phpstan.php
index 91dbb321c5..ddcbbe3fb8 100644
--- a/tests/PHPStan/Rules/Api/data/class-implements-out-of-phpstan.php
+++ b/tests/PHPStan/Rules/Api/data/class-implements-out-of-phpstan.php
@@ -234,6 +234,11 @@ public function isSmallerThanOrEqual(Type $otherType): \PHPStan\TrinaryLogic
 		// TODO: Implement isSmallerThanOrEqual() method.
 	}
 
+	public function isString(): \PHPStan\TrinaryLogic
+	{
+		// TODO: Implement isString() method.
+	}
+
 	public function isNumericString(): \PHPStan\TrinaryLogic
 	{
 		// TODO: Implement isNumericString() method.
diff --git a/tests/PHPStan/Rules/Operators/InvalidBinaryOperationRuleTest.php b/tests/PHPStan/Rules/Operators/InvalidBinaryOperationRuleTest.php
index b89c5e985e..0e88a2e23b 100644
--- a/tests/PHPStan/Rules/Operators/InvalidBinaryOperationRuleTest.php
+++ b/tests/PHPStan/Rules/Operators/InvalidBinaryOperationRuleTest.php
@@ -113,6 +113,134 @@ public function testRule(): void
 				'Binary operation "+" between stdClass and int results in an error.',
 				157,
 			],
+			[
+				'Binary operation "+" between non-empty-string and 10 results in an error.',
+				184,
+			],
+			[
+				'Binary operation "-" between non-empty-string and 10 results in an error.',
+				185,
+			],
+			[
+				'Binary operation "*" between non-empty-string and 10 results in an error.',
+				186,
+			],
+			[
+				'Binary operation "/" between non-empty-string and 10 results in an error.',
+				187,
+			],
+			[
+				'Binary operation "+" between 10 and non-empty-string results in an error.',
+				189,
+			],
+			[
+				'Binary operation "-" between 10 and non-empty-string results in an error.',
+				190,
+			],
+			[
+				'Binary operation "*" between 10 and non-empty-string results in an error.',
+				191,
+			],
+			[
+				'Binary operation "/" between 10 and non-empty-string results in an error.',
+				192,
+			],
+			[
+				'Binary operation "+" between string and 10 results in an error.',
+				194,
+			],
+			[
+				'Binary operation "-" between string and 10 results in an error.',
+				195,
+			],
+			[
+				'Binary operation "*" between string and 10 results in an error.',
+				196,
+			],
+			[
+				'Binary operation "/" between string and 10 results in an error.',
+				197,
+			],
+			[
+				'Binary operation "+" between 10 and string results in an error.',
+				199,
+			],
+			[
+				'Binary operation "-" between 10 and string results in an error.',
+				200,
+			],
+			[
+				'Binary operation "*" between 10 and string results in an error.',
+				201,
+			],
+			[
+				'Binary operation "/" between 10 and string results in an error.',
+				202,
+			],
+			[
+				'Binary operation "+" between class-string and 10 results in an error.',
+				204,
+			],
+			[
+				'Binary operation "-" between class-string and 10 results in an error.',
+				205,
+			],
+			[
+				'Binary operation "*" between class-string and 10 results in an error.',
+				206,
+			],
+			[
+				'Binary operation "/" between class-string and 10 results in an error.',
+				207,
+			],
+			[
+				'Binary operation "+" between 10 and class-string results in an error.',
+				209,
+			],
+			[
+				'Binary operation "-" between 10 and class-string results in an error.',
+				210,
+			],
+			[
+				'Binary operation "*" between 10 and class-string results in an error.',
+				211,
+			],
+			[
+				'Binary operation "/" between 10 and class-string results in an error.',
+				212,
+			],
+			[
+				'Binary operation "+" between literal-string and 10 results in an error.',
+				214,
+			],
+			[
+				'Binary operation "-" between literal-string and 10 results in an error.',
+				215,
+			],
+			[
+				'Binary operation "*" between literal-string and 10 results in an error.',
+				216,
+			],
+			[
+				'Binary operation "/" between literal-string and 10 results in an error.',
+				217,
+			],
+			[
+				'Binary operation "+" between 10 and literal-string results in an error.',
+				219,
+			],
+			[
+				'Binary operation "-" between 10 and literal-string results in an error.',
+				220,
+			],
+			[
+				'Binary operation "*" between 10 and literal-string results in an error.',
+				221,
+			],
+			[
+				'Binary operation "/" between 10 and literal-string results in an error.',
+				222,
+			],
 		]);
 	}
 
diff --git a/tests/PHPStan/Rules/Operators/data/invalid-binary.php b/tests/PHPStan/Rules/Operators/data/invalid-binary.php
index 9ea75a0589..c144298b6d 100644
--- a/tests/PHPStan/Rules/Operators/data/invalid-binary.php
+++ b/tests/PHPStan/Rules/Operators/data/invalid-binary.php
@@ -173,3 +173,78 @@ function (array $args) {
 function (array $args) {
 	isset($args['y']) ? $args + [] : $args;
 };
+
+/**
+ * @param non-empty-string $foo
+ * @param string $bar
+ * @param class-string $foobar
+ * @param literal-string $literalString
+ */
+function bug6624_should_error($foo, $bar, $foobar, $literalString) {
+	echo ($foo + 10);
+	echo ($foo - 10);
+	echo ($foo * 10);
+	echo ($foo / 10);
+
+	echo (10 + $foo);
+	echo (10 - $foo);
+	echo (10 * $foo);
+	echo (10 / $foo);
+
+	echo ($bar + 10);
+	echo ($bar - 10);
+	echo ($bar * 10);
+	echo ($bar / 10);
+
+	echo (10 + $bar);
+	echo (10 - $bar);
+	echo (10 * $bar);
+	echo (10 / $bar);
+
+	echo ($foobar + 10);
+	echo ($foobar - 10);
+	echo ($foobar * 10);
+	echo ($foobar / 10);
+
+	echo (10 + $foobar);
+	echo (10 - $foobar);
+	echo (10 * $foobar);
+	echo (10 / $foobar);
+
+	echo ($literalString + 10);
+	echo ($literalString - 10);
+	echo ($literalString * 10);
+	echo ($literalString / 10);
+
+	echo (10 + $literalString);
+	echo (10 - $literalString);
+	echo (10 * $literalString);
+	echo (10 / $literalString);
+}
+
+/**
+ * @param numeric-string $numericString
+ */
+function bug6624_no_error($numericString) {
+	echo ($numericString + 10);
+	echo ($numericString - 10);
+	echo ($numericString * 10);
+	echo ($numericString / 10);
+
+	echo (10 + $numericString);
+	echo (10 - $numericString);
+	echo (10 * $numericString);
+	echo (10 / $numericString);
+
+	$numericLiteral = "123";
+
+	echo ($numericLiteral + 10);
+	echo ($numericLiteral - 10);
+	echo ($numericLiteral * 10);
+	echo ($numericLiteral / 10);
+
+	echo (10 + $numericLiteral);
+	echo (10 - $numericLiteral);
+	echo (10 * $numericLiteral);
+	echo (10 / $numericLiteral);
+}