diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -3511,8 +3511,10 @@
 }
 
 /// Determine whether this alias template is "enable_if_t".
+/// libc++ sometimes uses "_EnableIf".
 static bool isEnableIfAliasTemplate(TypeAliasTemplateDecl *AliasTemplate) {
-  return AliasTemplate->getName().equals("enable_if_t");
+  return AliasTemplate->getName().equals("enable_if_t") ||
+         AliasTemplate->getName().equals("_EnableIf");
 }
 
 /// Collect all of the separable terms in the given condition, which