diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -4693,6 +4693,9 @@
 }
 
 /// Reference initialization without resolving overloaded functions.
+///
+/// We also can get here in C if we call a builtin which is declared as
+/// a function with a parameter of reference type (such as __builtin_va_end()).
 static void TryReferenceInitializationCore(Sema &S,
                                            const InitializedEntity &Entity,
                                            const InitializationKind &Kind,
@@ -4769,15 +4772,20 @@
     // an rvalue. DR1287 removed the "implicitly" here.
     if (RefRelationship == Sema::Ref_Incompatible && T2->isRecordType() &&
         (isLValueRef || InitCategory.isRValue())) {
-      ConvOvlResult = TryRefInitWithConversionFunction(
-          S, Entity, Kind, Initializer, /*AllowRValues*/ isRValueRef,
-          /*IsLValueRef*/ isLValueRef, Sequence);
-      if (ConvOvlResult == OR_Success)
-        return;
-      if (ConvOvlResult != OR_No_Viable_Function)
-        Sequence.SetOverloadFailure(
-            InitializationSequence::FK_ReferenceInitOverloadFailed,
-            ConvOvlResult);
+      if (S.getLangOpts().CPlusPlus) {
+        // Try conversion functions only for C++.
+        ConvOvlResult = TryRefInitWithConversionFunction(
+            S, Entity, Kind, Initializer, /*AllowRValues*/ isRValueRef,
+            /*IsLValueRef*/ isLValueRef, Sequence);
+        if (ConvOvlResult == OR_Success)
+          return;
+        if (ConvOvlResult != OR_No_Viable_Function)
+          Sequence.SetOverloadFailure(
+              InitializationSequence::FK_ReferenceInitOverloadFailed,
+              ConvOvlResult);
+      } else {
+        ConvOvlResult = OR_No_Viable_Function;
+      }
     }
   }
 
diff --git a/clang/test/Sema/init-ref-c.c b/clang/test/Sema/init-ref-c.c
new file mode 100644
--- /dev/null
+++ b/clang/test/Sema/init-ref-c.c
@@ -0,0 +1,7 @@
+// RUN: %clang_cc1 -triple arm-unknown-gnu -fsyntax-only -verify %s
+
+void f() {
+  struct EmptyStruct {};
+  struct EmptyStruct S;
+  __builtin_va_end(S); // no-crash, expected-error {{non-const lvalue reference to type '__builtin_va_list' cannot bind to a value of unrelated type 'struct EmptyStruct'}}
+}
\ No newline at end of file