diff --git a/lib/ClangImporter/ImportType.cpp b/lib/ClangImporter/ImportType.cpp
index 7871ee6977ce7..35ef5f19642e2 100644
--- a/lib/ClangImporter/ImportType.cpp
+++ b/lib/ClangImporter/ImportType.cpp
@@ -787,7 +787,7 @@ namespace {
         }
 
         static const llvm::StringLiteral vaListNames[] = {
-          "va_list", "__gnuc_va_list", "__va_list"
+          "va_list", "__gnuc_va_list", "__isoc_va_list", "__va_list"
         };
 
         ImportHint hint = ImportHint::None;
diff --git a/lib/ClangImporter/MappedTypes.def b/lib/ClangImporter/MappedTypes.def
index c1a8c8039dcd1..7f11008619a99 100644
--- a/lib/ClangImporter/MappedTypes.def
+++ b/lib/ClangImporter/MappedTypes.def
@@ -128,6 +128,7 @@ MAP_STDLIB_TYPE("u_int64_t", UnsignedInt, 64, "UInt64", false, DoNothing)
 // There's an explicit workaround in ImportType.cpp's VisitDecayedType for that.
 MAP_STDLIB_TYPE("va_list", VaList, 0, "CVaListPointer", false, DoNothing)
 MAP_STDLIB_TYPE("__gnuc_va_list", VaList, 0, "CVaListPointer", false, DoNothing)
+MAP_STDLIB_TYPE("__isoc_va_list", VaList, 0, "CVaListPointer", false, DoNothing)
 MAP_STDLIB_TYPE("__va_list", VaList, 0, "CVaListPointer", false, DoNothing)
 
 // libkern/OSTypes.h types.
diff --git a/test/Interop/C/va_list/Inputs/module.modulemap b/test/Interop/C/va_list/Inputs/module.modulemap
new file mode 100644
index 0000000000000..be337a926c6bb
--- /dev/null
+++ b/test/Interop/C/va_list/Inputs/module.modulemap
@@ -0,0 +1,4 @@
+module ImportCVAList {
+  header "va_list.h"
+  export *
+}
diff --git a/test/Interop/C/va_list/Inputs/va_list.h b/test/Interop/C/va_list/Inputs/va_list.h
new file mode 100644
index 0000000000000..2601016af7088
--- /dev/null
+++ b/test/Interop/C/va_list/Inputs/va_list.h
@@ -0,0 +1,10 @@
+#include <stdarg.h>
+
+typedef va_list __gnuc_va_list;
+typedef va_list __isoc_va_list;
+typedef va_list __va_list;
+
+va_list va;
+__gnuc_va_list gnu;
+__isoc_va_list isoC;
+__va_list underscore;
diff --git a/test/Interop/C/va_list/va_list.swift b/test/Interop/C/va_list/va_list.swift
new file mode 100644
index 0000000000000..859f94343fe8e
--- /dev/null
+++ b/test/Interop/C/va_list/va_list.swift
@@ -0,0 +1,6 @@
+// RUN: %target-swift-ide-test -print-module -module-to-print=ImportCVAList -I %S/Inputs -source-filename=x | %FileCheck %s
+
+// CHECK: var va: CVaListPointer
+// CHECK: var gnu: CVaListPointer
+// CHECK: var isoC: CVaListPointer
+// CHECK: var underscore: CVaListPointer