diff --git a/src/language-js/parse/postprocess/index.js b/src/language-js/parse/postprocess/index.js
index cc07c76bc..d9b567eb6 100644
--- a/src/language-js/parse/postprocess/index.js
+++ b/src/language-js/parse/postprocess/index.js
@@ -112,6 +112,23 @@ function postprocess(ast, options) {
           }
         }
         break;
+      case "DeclareInterface":
+      case "InterfaceDeclaration":
+      case "TSInterfaceDeclaration":
+        if (isNonEmptyArray(node.mixins)) {
+          throwSyntaxError(
+            node.mixins[0],
+            "Interface declaration cannot have 'mixins' clause."
+          );
+        }
+        if (isNonEmptyArray(node.implements)) {
+          throwSyntaxError(
+            node.implements[0],
+            "Interface declaration cannot have 'implements' clause."
+          );
+        }
+        break;
+
       case "TSPropertySignature":
         if (node.initializer) {
           throwSyntaxError(
diff --git a/src/language-js/traverse/visitor-keys.evaluate.js b/src/language-js/traverse/visitor-keys.evaluate.js
index a0181bb03..0680fbb17 100644
--- a/src/language-js/traverse/visitor-keys.evaluate.js
+++ b/src/language-js/traverse/visitor-keys.evaluate.js
@@ -57,6 +57,8 @@ const excludeKeys = {
   // TODO: Remove `types` when babel changes AST of `TupleTypeAnnotation`
   // Flow parser changed `.types` to `.elementTypes` https://github.com/facebook/flow/commit/5b60e6a81dc277dfab2e88fa3737a4dc9aafdcab
   // TupleTypeAnnotation: ["types"],
+  DeclareInterface: ["mixins", "implements"],
+  InterfaceDeclaration: ["mixins", "implements"],
 
   // TypeScript
   TSPropertySignature: ["initializer"],
diff --git a/tests/format/misc/errors/flow/declare-export-interface/__snapshots__/jsfmt.spec.js.snap b/tests/format/misc/errors/flow/declare-export-interface/__snapshots__/jsfmt.spec.js.snap
deleted file mode 100644
index d7366192f..000000000
--- a/tests/format/misc/errors/flow/declare-export-interface/__snapshots__/jsfmt.spec.js.snap
+++ /dev/null
@@ -1,13 +0,0 @@
-// Jest Snapshot v1, https://goo.gl/fbAQLP
-
-exports[`snippet: #0 [babel-flow] format 1`] = `
-"\`declare export interface\` is not supported. Use \`export interface\` instead. (1:16)
-> 1 | declare export interface A {}
-    |                ^"
-`;
-
-exports[`snippet: #0 [flow] format 1`] = `
-"\`declare export interface\` is not supported. Use \`export interface\` instead. (1:16)
-> 1 | declare export interface A {}
-    |                ^^^^^^^^^"
-`;
diff --git a/tests/format/misc/errors/flow/declare-export-interface/jsfmt.spec.js b/tests/format/misc/errors/flow/declare-export-interface/jsfmt.spec.js
deleted file mode 100644
index be0643c1b..000000000
--- a/tests/format/misc/errors/flow/declare-export-interface/jsfmt.spec.js
+++ /dev/null
@@ -1,7 +0,0 @@
-run_spec(
-  {
-    importMeta: import.meta,
-    snippets: ["declare export interface A {}"],
-  },
-  ["flow", "babel-flow"]
-);
diff --git a/tests/format/misc/errors/flow/interface/__snapshots__/jsfmt.spec.js.snap b/tests/format/misc/errors/flow/interface/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000..0330abc95
--- /dev/null
+++ b/tests/format/misc/errors/flow/interface/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,61 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`snippet: #0 [babel-flow] format 1`] = `
+"\`declare export interface\` is not supported. Use \`export interface\` instead. (1:16)
+> 1 | declare export interface A {}
+    |                ^"
+`;
+
+exports[`snippet: #0 [flow] format 1`] = `
+"\`declare export interface\` is not supported. Use \`export interface\` instead. (1:16)
+> 1 | declare export interface A {}
+    |                ^^^^^^^^^"
+`;
+
+exports[`snippet: #1 [babel-flow] format 1`] = `
+"Interface declaration cannot have 'mixins' clause. (1:20)
+> 1 | interface A mixins B {}
+    |                    ^"
+`;
+
+exports[`snippet: #1 [flow] format 1`] = `
+"Unexpected identifier, expected the token \`{\` (1:13)
+> 1 | interface A mixins B {}
+    |             ^^^^^^"
+`;
+
+exports[`snippet: #2 [babel-flow] format 1`] = `
+"Interface declaration cannot have 'implements' clause. (1:24)
+> 1 | interface A implements B {}
+    |                        ^"
+`;
+
+exports[`snippet: #2 [flow] format 1`] = `
+"Unexpected identifier, expected the token \`{\` (1:13)
+> 1 | interface A implements B {}
+    |             ^^^^^^^^^^"
+`;
+
+exports[`snippet: #3 [babel-flow] format 1`] = `
+"Interface declaration cannot have 'mixins' clause. (1:28)
+> 1 | declare interface A mixins B {}
+    |                            ^"
+`;
+
+exports[`snippet: #3 [flow] format 1`] = `
+"Unexpected identifier, expected the token \`{\` (1:21)
+> 1 | declare interface A mixins B {}
+    |                     ^^^^^^"
+`;
+
+exports[`snippet: #4 [babel-flow] format 1`] = `
+"Interface declaration cannot have 'implements' clause. (1:32)
+> 1 | declare interface A implements B {}
+    |                                ^"
+`;
+
+exports[`snippet: #4 [flow] format 1`] = `
+"Unexpected identifier, expected the token \`{\` (1:21)
+> 1 | declare interface A implements B {}
+    |                     ^^^^^^^^^^"
+`;
diff --git a/tests/format/misc/errors/flow/interface/jsfmt.spec.js b/tests/format/misc/errors/flow/interface/jsfmt.spec.js
new file mode 100644
index 000000000..787aab314
--- /dev/null
+++ b/tests/format/misc/errors/flow/interface/jsfmt.spec.js
@@ -0,0 +1,16 @@
+run_spec(
+  {
+    importMeta: import.meta,
+    snippets: [
+      // Not allowed
+      "declare export interface A {}",
+
+      // Can't have mixins nor implements
+      "interface A mixins B {}",
+      "interface A implements B {}",
+      "declare interface A mixins B {}",
+      "declare interface A implements B {}",
+    ],
+  },
+  ["flow", "babel-flow"]
+);
diff --git a/tests/format/misc/errors/typescript/interface/__snapshots__/jsfmt.spec.js.snap b/tests/format/misc/errors/typescript/interface/__snapshots__/jsfmt.spec.js.snap
index 37519d6f6..5e486bc57 100644
--- a/tests/format/misc/errors/typescript/interface/__snapshots__/jsfmt.spec.js.snap
+++ b/tests/format/misc/errors/typescript/interface/__snapshots__/jsfmt.spec.js.snap
@@ -11,3 +11,27 @@ exports[`snippet: #0 [typescript] format 1`] = `
 > 1 | interface I { x: number = 1;}
     |                           ^"
 `;
+
+exports[`snippet: #1 [babel-ts] format 1`] = `
+"Unexpected token, expected "{" (1:13)
+> 1 | interface A mixins B {}
+    |             ^"
+`;
+
+exports[`snippet: #1 [typescript] format 1`] = `
+"'{' expected. (1:13)
+> 1 | interface A mixins B {}
+    |             ^"
+`;
+
+exports[`snippet: #2 [babel-ts] format 1`] = `
+"Unexpected token, expected "{" (1:13)
+> 1 | interface A implements B {}
+    |             ^"
+`;
+
+exports[`snippet: #2 [typescript] format 1`] = `
+"Interface declaration cannot have 'implements' clause. (1:24)
+> 1 | interface A implements B {}
+    |                        ^"
+`;
diff --git a/tests/format/misc/errors/typescript/interface/jsfmt.spec.js b/tests/format/misc/errors/typescript/interface/jsfmt.spec.js
index a1d5dde7e..71ebb8528 100644
--- a/tests/format/misc/errors/typescript/interface/jsfmt.spec.js
+++ b/tests/format/misc/errors/typescript/interface/jsfmt.spec.js
@@ -4,6 +4,9 @@ run_spec(
     snippets: [
       // Invalid initializer
       "interface I { x: number = 1;}",
+      // Can't have mixins nor implements
+      "interface A mixins B {}",
+      "interface A implements B {}",
     ],
   },
   ["babel-ts", "typescript"]
diff --git a/tests/unit/__snapshots__/visitor-keys.js.snap b/tests/unit/__snapshots__/visitor-keys.js.snap
index a056505b4..7b25170c7 100644
--- a/tests/unit/__snapshots__/visitor-keys.js.snap
+++ b/tests/unit/__snapshots__/visitor-keys.js.snap
@@ -176,8 +176,6 @@ exports[`visitor keys estree 1`] = `
     "id",
     "typeParameters",
     "extends",
-    "mixins",
-    "implements",
     "body",
   ],
   "DeclareModule": [
@@ -375,8 +373,6 @@ exports[`visitor keys estree 1`] = `
     "id",
     "typeParameters",
     "extends",
-    "mixins",
-    "implements",
     "body",
   ],
   "InterfaceExtends": [