diff --git a/src/type/__tests__/validation-test.ts b/src/type/__tests__/validation-test.ts
index 3c2fe21500..ca07a220d6 100644
--- a/src/type/__tests__/validation-test.ts
+++ b/src/type/__tests__/validation-test.ts
@@ -747,7 +747,7 @@ describe('Type System: Union types must be valid', () => {
     ]);
   });
 
-  it('rejects a Union type with non-Object members types', () => {
+  it('rejects a Union type with non-Object member types', () => {
     let schema = buildSchema(`
       type Query {
         test: BadUnion
@@ -807,6 +807,47 @@ describe('Type System: Union types must be valid', () => {
       ]);
     }
   });
+
+  it('rejects a Union type with duplicate non-Object member types', () => {
+    let schema = buildSchema(`
+      type Query {
+        test: BadUnion
+      }
+
+      type TypeA {
+        field: String
+      }
+
+      union BadUnion =
+        | Int
+        | String
+        | TypeA
+        | Int
+        | String
+    `);
+
+    schema = extendSchema(schema, parse('extend union BadUnion = Int'));
+
+    expectJSON(validateSchema(schema)).toDeepEqual([
+      {
+        message:
+          'Union type BadUnion can only include Object types, it cannot include Int.',
+        locations: [
+          { line: 11, column: 11 },
+          { line: 14, column: 11 },
+          { line: 1, column: 25 },
+        ],
+      },
+      {
+        message:
+          'Union type BadUnion can only include Object types, it cannot include String.',
+        locations: [
+          { line: 12, column: 11 },
+          { line: 15, column: 11 },
+        ],
+      },
+    ]);
+  });
 });
 
 describe('Type System: Input Objects must have fields', () => {
diff --git a/src/type/validate.ts b/src/type/validate.ts
index 3a69a8c6eb..b4e1568beb 100644
--- a/src/type/validate.ts
+++ b/src/type/validate.ts
@@ -480,7 +480,20 @@ function validateUnionMembers(
   }
 
   const includedTypeNames = new Set<string>();
+  const includedInvalidTypes = new Set<string>();
   for (const memberType of memberTypes) {
+    if (!isObjectType(memberType)) {
+      const typeString = inspect(memberType);
+      if (!includedInvalidTypes.has(typeString)) {
+        context.reportError(
+          `Union type ${union.name} can only include Object types, ` +
+            `it cannot include ${inspect(memberType)}.`,
+          getUnionMemberTypeNodes(union, String(memberType)),
+        );
+        includedInvalidTypes.add(typeString);
+      }
+      continue;
+    }
     if (includedTypeNames.has(memberType.name)) {
       context.reportError(
         `Union type ${union.name} can only include type ${memberType} once.`,
@@ -489,13 +502,6 @@ function validateUnionMembers(
       continue;
     }
     includedTypeNames.add(memberType.name);
-    if (!isObjectType(memberType)) {
-      context.reportError(
-        `Union type ${union.name} can only include Object types, ` +
-          `it cannot include ${inspect(memberType)}.`,
-        getUnionMemberTypeNodes(union, String(memberType)),
-      );
-    }
   }
 }