diff --git a/src/rules/interfaceNameRule.ts b/src/rules/interfaceNameRule.ts
index b33281c4dbe..32f169f5e2c 100644
--- a/src/rules/interfaceNameRule.ts
+++ b/src/rules/interfaceNameRule.ts
@@ -19,7 +19,7 @@ import * as utils from "tsutils";
 import * as ts from "typescript";
 
 import * as Lint from "../index";
-import { isUpperCase } from "../utils";
+import { isLowerCase, isUpperCase } from "../utils";
 
 const OPTION_ALWAYS = "always-prefix";
 const OPTION_NEVER = "never-prefix";
@@ -62,10 +62,12 @@ function walk(ctx: Lint.WalkContext<{ never: boolean }>): void {
     return ts.forEachChild(ctx.sourceFile, function cb(node: ts.Node): void {
         if (utils.isInterfaceDeclaration(node)) {
             const { name } = node;
-            if (never && hasPrefixI(name.text)) {
-                ctx.addFailureAtNode(name, Rule.FAILURE_STRING_NO_PREFIX);
-            } else if (!never && name.text[0] !== "I") {
-                ctx.addFailureAtNode(name, Rule.FAILURE_STRING);
+            if (!cantDecide(name.text)) {
+                if (never && hasPrefixI(name.text)) {
+                    ctx.addFailureAtNode(name, Rule.FAILURE_STRING_NO_PREFIX);
+                } else if (!never && !hasPrefixI(name.text)) {
+                    ctx.addFailureAtNode(name, Rule.FAILURE_STRING);
+                }
             }
         } else {
             return ts.forEachChild(node, cb);
@@ -74,6 +76,12 @@ function walk(ctx: Lint.WalkContext<{ never: boolean }>): void {
 }
 
 function hasPrefixI(name: string): boolean {
-    // Allow IndexedDB interfaces
-    return name.length >= 2 && name[0] === "I" && isUpperCase(name[1]) && !name.startsWith("IDB");
+    return name.length >= 3 && name[0] === "I" && !isLowerCase(name[1]) && !isUpperCase(name[2]);
+}
+
+function cantDecide(name: string): boolean {
+    return (
+        (name.length === 2 && name[0] === "I" && !isLowerCase(name[1])) ||
+        (name.length >= 2 && name[0] === "I" && !isLowerCase(name[1]) && !isLowerCase(name[2]))
+    );
 }
diff --git a/test/rules/interface-name/always-prefix/test.ts.lint b/test/rules/interface-name/always-prefix/test.ts.lint
index df81902d1d8..7dda122e691 100644
--- a/test/rules/interface-name/always-prefix/test.ts.lint
+++ b/test/rules/interface-name/always-prefix/test.ts.lint
@@ -2,7 +2,20 @@
 interface IOptions {
 }
 
+interface ID {
+}
+
+interface IABC {
+}
+
+interface IDBFactory {
+}
+
 // invalid code
 interface Options {
           ~~~~~~~   [interface name must start with a capitalized I]
 }
+
+interface Incomplete {
+          ~~~~~~~~~~   [interface name must start with a capitalized I]
+}
diff --git a/test/rules/interface-name/never-prefix/test.ts.lint b/test/rules/interface-name/never-prefix/test.ts.lint
index 84d59f63b1f..f6afc38f412 100644
--- a/test/rules/interface-name/never-prefix/test.ts.lint
+++ b/test/rules/interface-name/never-prefix/test.ts.lint
@@ -5,9 +5,18 @@ interface Index {
 interface I {
 }
 
+interface ID {
+}
+
+interface IABC {
+}
+
 interface IDBFactory {
 }
 
+interface I18nFactory {
+}
+
 interface ABC {
 }