diff --git a/clang/lib/AST/Interp/InterpBuiltin.cpp b/clang/lib/AST/Interp/InterpBuiltin.cpp
index 8bbe881bb4b92..7e29d6183bdad 100644
--- a/clang/lib/AST/Interp/InterpBuiltin.cpp
+++ b/clang/lib/AST/Interp/InterpBuiltin.cpp
@@ -533,11 +533,12 @@ static bool interp__builtin_rotate(InterpState &S, CodePtr OpPC,
                                    const InterpFrame *Frame,
                                    const Function *Func, const CallExpr *Call,
                                    bool Right) {
-  PrimType ArgT = *S.getContext().classify(Call->getArg(0)->getType());
-  assert(ArgT == *S.getContext().classify(Call->getArg(1)->getType()));
+  PrimType AmountT = *S.getContext().classify(Call->getArg(1)->getType());
+  PrimType ValueT = *S.getContext().classify(Call->getArg(0)->getType());
 
-  APSInt Amount = peekToAPSInt(S.Stk, ArgT);
-  APSInt Value = peekToAPSInt(S.Stk, ArgT, align(primSize(ArgT)) * 2);
+  APSInt Amount = peekToAPSInt(S.Stk, AmountT);
+  APSInt Value = peekToAPSInt(
+      S.Stk, ValueT, align(primSize(AmountT)) + align(primSize(ValueT)));
 
   APSInt Result;
   if (Right)
diff --git a/clang/test/AST/Interp/ms.cpp b/clang/test/AST/Interp/ms.cpp
new file mode 100644
index 0000000000000..99716e90c7a1d
--- /dev/null
+++ b/clang/test/AST/Interp/ms.cpp
@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -verify=ref,both %s -fms-extensions
+// RUN: %clang_cc1 -verify=expected,both %s -fexperimental-new-constant-interpreter -fms-extensions
+
+// ref-no-diagnostics
+// expected-no-diagnostics
+
+/// Used to assert because the two parameters to _rotl do not have the same type.
+static_assert(_rotl(0x01, 5) == 32);