diff --git a/lib/parser/builders/default.rb b/lib/parser/builders/default.rb
index 860d84e84..5e3cd59be 100644
--- a/lib/parser/builders/default.rb
+++ b/lib/parser/builders/default.rb
@@ -1239,8 +1239,10 @@ def unless_guard(unless_t, unless_body)
 
     def match_var(name_t)
       name = value(name_t).to_sym
+      name_l = loc(name_t)
 
-      check_duplicate_pattern_variable(name, loc(name_t))
+      check_lvar_name(name, name_l)
+      check_duplicate_pattern_variable(name, name_l)
       @parser.static_env.declare(name)
 
       n(:match_var, [ name ],
@@ -1253,6 +1255,7 @@ def match_hash_var(name_t)
       expr_l = loc(name_t)
       name_l = expr_l.adjust(end_pos: -1)
 
+      check_lvar_name(name, name_l)
       check_duplicate_pattern_variable(name, name_l)
       @parser.static_env.declare(name)
 
@@ -1293,6 +1296,9 @@ def match_hash_var_from_str(begin_t, strings, end_t)
           Source::Map::Variable.new(name_l, expr_l))
       when :begin
         match_hash_var_from_str(begin_t, string.children, end_t)
+      else
+        # we only can get here if there is an interpolation, e.g., ``in "#{ a }":`
+        diagnostic :error, :pm_interp_in_var_name, nil, loc(begin_t).join(loc(end_t))
       end
     end
 
diff --git a/test/test_parser.rb b/test/test_parser.rb
index 5fc1e5111..64f631f6b 100644
--- a/test/test_parser.rb
+++ b/test/test_parser.rb
@@ -8934,6 +8934,22 @@ def test_pattern_matching_hash_with_string_interpolation_keys
       %q{           ~~~~~~~ location},
       SINCE_2_7
     )
+
+    assert_diagnoses(
+      [:error, :pm_interp_in_var_name],
+      %q{case a; in "#{a}": 1; end},
+      %q{           ~~~~~~~ location},
+      SINCE_2_7
+    )
+  end
+
+  def test_pattern_matching_invalid_lvar_name
+    assert_diagnoses(
+      [:error, :lvar_name, { name: :a? }],
+      %q{case a; in a?:; end},
+      %q{           ~~ location},
+      SINCE_2_7
+    )
   end
 
   def test_pattern_matching_keyword_variable