diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 353356c208b..6e249c3977d 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -20487,7 +20487,7 @@ namespace ts {
                             errorMessage = Diagnostics.Class_0_defines_instance_member_accessor_1_but_extended_class_2_defines_it_as_instance_member_function;
                         }
 
-                        error(derived.valueDeclaration.name, errorMessage, typeToString(baseType), symbolToString(base), typeToString(type));
+                        error(derived.valueDeclaration.name || derived.valueDeclaration, errorMessage, typeToString(baseType), symbolToString(base), typeToString(type));
                     }
                 }
             }
diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index d7d93f49ee7..0971adfc098 100644
--- a/src/compiler/program.ts
+++ b/src/compiler/program.ts
@@ -930,20 +930,22 @@ namespace ts {
          */
         function shouldReportDiagnostic(diagnostic: Diagnostic) {
             const { file, start } = diagnostic;
-            const lineStarts = getLineStarts(file);
-            let { line } = computeLineAndCharacterOfPosition(lineStarts, start);
-            while (line > 0) {
-                const previousLineText = file.text.slice(lineStarts[line - 1], lineStarts[line]);
-                const result = ignoreDiagnosticCommentRegEx.exec(previousLineText);
-                if (!result) {
-                    // non-empty line
-                    return true;
+            if (file) {
+                const lineStarts = getLineStarts(file);
+                let { line } = computeLineAndCharacterOfPosition(lineStarts, start);
+                while (line > 0) {
+                    const previousLineText = file.text.slice(lineStarts[line - 1], lineStarts[line]);
+                    const result = ignoreDiagnosticCommentRegEx.exec(previousLineText);
+                    if (!result) {
+                        // non-empty line
+                        return true;
+                    }
+                    if (result[3]) {
+                        // @ts-ignore
+                        return false;
+                    }
+                    line--;
                 }
-                if (result[3]) {
-                    // @ts-ignore
-                    return false;
-                }
-                line--;
             }
             return true;
         }
diff --git a/tests/baselines/reference/checkJsFiles_noErrorLocation.errors.txt b/tests/baselines/reference/checkJsFiles_noErrorLocation.errors.txt
new file mode 100644
index 00000000000..758b295a49d
--- /dev/null
+++ b/tests/baselines/reference/checkJsFiles_noErrorLocation.errors.txt
@@ -0,0 +1,25 @@
+tests/cases/compiler/a.js(14,5): error TS2424: Class 'A' defines instance member function 'foo', but extended class 'B' defines it as instance member property.
+
+
+==== tests/cases/compiler/a.js (1 errors) ====
+    // @ts-check
+    class A {
+      constructor() {
+    
+      }
+      foo() {
+        return 4;
+      }
+    }
+    
+    class B extends A {
+      constructor() {
+        super();
+        this.foo = () => 3;
+        ~~~~~~~~~~~~~~~~~~
+!!! error TS2424: Class 'A' defines instance member function 'foo', but extended class 'B' defines it as instance member property.
+      }
+    }
+    
+    const i = new B();
+    i.foo();
\ No newline at end of file
diff --git a/tests/cases/compiler/checkJsFiles_noErrorLocation.ts b/tests/cases/compiler/checkJsFiles_noErrorLocation.ts
new file mode 100644
index 00000000000..a0b12c47115
--- /dev/null
+++ b/tests/cases/compiler/checkJsFiles_noErrorLocation.ts
@@ -0,0 +1,24 @@
+// @allowJs: true
+// @checkJs: true
+// @noEmit: true
+
+// @fileName: a.js
+// @ts-check
+class A {
+  constructor() {
+
+  }
+  foo() {
+    return 4;
+  }
+}
+
+class B extends A {
+  constructor() {
+    super();
+    this.foo = () => 3;
+  }
+}
+
+const i = new B();
+i.foo();
\ No newline at end of file