diff --git a/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp b/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
--- a/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
+++ b/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
@@ -1672,9 +1672,8 @@
   /// This function either returns the value set earlier with setShadow,
   /// or extracts if from ParamTLS (for function arguments).
   Value *getShadow(Value *V) {
-    if (!PropagateShadow) return getCleanShadow(V);
     if (Instruction *I = dyn_cast<Instruction>(V)) {
-      if (I->getMetadata("nosanitize"))
+      if (!PropagateShadow || I->getMetadata("nosanitize"))
         return getCleanShadow(V);
       // For instructions the shadow is already stored in the map.
       Value *Shadow = ShadowMap[V];
@@ -1686,7 +1685,7 @@
       return Shadow;
     }
     if (UndefValue *U = dyn_cast<UndefValue>(V)) {
-      Value *AllOnes = PoisonUndef ? getPoisonedShadow(V) : getCleanShadow(V);
+      Value *AllOnes = (PropagateShadow && PoisonUndef) ? getPoisonedShadow(V) : getCleanShadow(V);
       LLVM_DEBUG(dbgs() << "Undef: " << *U << " ==> " << *AllOnes << "\n");
       (void)U;
       return AllOnes;
@@ -1723,7 +1722,7 @@
                                    /*isStore*/ true)
                     .first;
             // TODO(glider): need to copy origins.
-            if (Overflow) {
+            if (!PropagateShadow || Overflow) {
               // ParamTLS overflow.
               EntryIRB.CreateMemSet(
                   CpShadowPtr, Constant::getNullValue(EntryIRB.getInt8Ty()),
@@ -1738,7 +1737,7 @@
             }
           }
 
-          if (Overflow || FArg.hasByValAttr() ||
+          if (!PropagateShadow || Overflow || FArg.hasByValAttr() ||
               (MS.EagerChecks && FArg.hasAttribute(Attribute::NoUndef))) {
             *ShadowPtr = getCleanShadow(V);
             setOrigin(A, getCleanOrigin());
diff --git a/llvm/test/Instrumentation/MemorySanitizer/byval.ll b/llvm/test/Instrumentation/MemorySanitizer/byval.ll
--- a/llvm/test/Instrumentation/MemorySanitizer/byval.ll
+++ b/llvm/test/Instrumentation/MemorySanitizer/byval.ll
@@ -25,6 +25,7 @@
 define i16 @ByValArgumentNoSanitize(i32 %unused, i16* byval(i16) %p) {
 ; CHECK-LABEL: @ByValArgumentNoSanitize(
 ; CHECK-NEXT:  entry:
+; CHECK:         call void @llvm.memset.p0i8.i64(i8* align 2 {{.*}}, i8 0, i64 2, i1 false)
 ; CHECK:         %x = load i16, i16* %p
 ; CHECK:         store i16 0, i16* bitcast ([100 x i64]* @__msan_retval_tls to i16*), align 8
 ; CHECK-NEXT:    store i32 0, i32* @__msan_retval_origin_tls, align 4
@@ -49,10 +50,10 @@
   ret void
 }
 
-; FIXME: Shadow of byval pointee is not set.
 define void @ByValForwardNoSanitize(i32 %unused, i16* byval(i16) %p) {
 ; CHECK-LABEL: @ByValForwardNoSanitize(
 ; CHECK-NEXT:  entry:
+; CHECK:         call void @llvm.memset.p0i8.i64(i8* align 2 {{.*}}, i8 0, i64 2, i1 false)
 ; CHECK:         store i64 0, i64* getelementptr inbounds ([100 x i64], [100 x i64]* @__msan_param_tls, i32 0, i32 0), align 8
 ; CHECK-NEXT:    call void @Fn(i16*
 ; CHECK-NEXT:    ret void