Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td
+++ include/clang/Basic/DiagnosticSemaKinds.td
@@ -6156,6 +6156,10 @@
   "comparison of two values with different enumeration types"
   "%diff{ ($ and $)|}0,1">,
   InGroup<EnumCompare>;
+def warn_conditional_mixed_enum_types : Warning<
+  "enumeration type mismatch in conditional expression"
+  "%diff{ ($ and $)|}0,1">,
+  InGroup<EnumCompare>;
 def warn_comparison_of_mixed_enum_types_switch : Warning<
   "comparison of two values with different enumeration types in switch statement"
   "%diff{ ($ and $)|}0,1">,
Index: lib/Sema/SemaChecking.cpp
===================================================================
--- lib/Sema/SemaChecking.cpp
+++ lib/Sema/SemaChecking.cpp
@@ -11256,6 +11256,34 @@
   return true;
 }
 
+static void checkConditionalWithEnumTypes(Sema &S, SourceLocation Loc,
+                                          Expr *LHS, Expr *RHS) {
+  QualType LHSStrippedType = LHS->IgnoreParenImpCasts()->getType();
+  QualType RHSStrippedType = RHS->IgnoreParenImpCasts()->getType();
+
+  const EnumType *LHSEnumType = LHSStrippedType->getAs<EnumType>();
+  if (!LHSEnumType)
+    return;
+  const EnumType *RHSEnumType = RHSStrippedType->getAs<EnumType>();
+  if (!RHSEnumType)
+    return;
+
+  // Ignore anonymous enums.
+  if (!LHSEnumType->getDecl()->getIdentifier() &&
+      !LHSEnumType->getDecl()->getTypedefNameForAnonDecl())
+    return;
+  if (!RHSEnumType->getDecl()->getIdentifier() &&
+      !RHSEnumType->getDecl()->getTypedefNameForAnonDecl())
+    return;
+
+  if (S.Context.hasSameUnqualifiedType(LHSStrippedType, RHSStrippedType))
+    return;
+
+  S.Diag(Loc, diag::warn_conditional_mixed_enum_types)
+      << LHSStrippedType << RHSStrippedType << LHS->getSourceRange()
+      << RHS->getSourceRange();
+}
+
 static void DiagnoseIntInBoolContext(Sema &S, Expr *E) {
   E = E->IgnoreParenImpCasts();
   SourceLocation ExprLoc = E->getExprLoc();
@@ -11754,6 +11782,8 @@
   bool Suspicious = false;
   CheckConditionalOperand(S, E->getTrueExpr(), T, CC, Suspicious);
   CheckConditionalOperand(S, E->getFalseExpr(), T, CC, Suspicious);
+  checkConditionalWithEnumTypes(S, E->getBeginLoc(), E->getTrueExpr(),
+                                E->getFalseExpr());
 
   if (T->isBooleanType())
     DiagnoseIntInBoolContext(S, E);