diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp
index d17ca780fce1..5b0664101f03 100644
--- a/clang/lib/CodeGen/CGBuiltin.cpp
+++ b/clang/lib/CodeGen/CGBuiltin.cpp
@@ -1264,9 +1264,13 @@ unsigned CodeGenFunction::GetPointeeAlignment(const Expr *Addr) {
   // Check if the type is a pointer.  The implicit cast operand might not be.
   while (Addr->getType()->isPointerType()) {
     QualType PtTy = Addr->getType()->getPointeeType();
-    unsigned NewA = getContext().getTypeAlignInChars(PtTy).getQuantity();
-    if (NewA > Align)
-      Align = NewA;
+    
+    // Can't get alignment of incomplete types.
+    if (!PtTy->isIncompleteType()) {
+      unsigned NewA = getContext().getTypeAlignInChars(PtTy).getQuantity();
+      if (NewA > Align)
+        Align = NewA;
+    }
 
     // If the address is an implicit cast, repeat with the cast operand.
     if (const ImplicitCastExpr *CastAddr = dyn_cast<ImplicitCastExpr>(Addr)) {
diff --git a/clang/test/CodeGen/builtin-memfns.c b/clang/test/CodeGen/builtin-memfns.c
index fb4d7200752d..e4389f621142 100644
--- a/clang/test/CodeGen/builtin-memfns.c
+++ b/clang/test/CodeGen/builtin-memfns.c
@@ -48,3 +48,14 @@ void test5(char *P, char *Q) {
 int test6(char *X) {
   return __builtin___memcpy_chk(X, X, 42, 42) != 0;
 }
+
+// CHECK: @test7
+// PR12094
+int test7(int *p) {
+  // CHECK: call void @llvm.memset{{.*}}256, i32 4, i1 false)
+  __builtin_memset(p, 0, 256);  // Should be alignment = 4
+  struct snd_pcm_hw_params_t* hwparams;  // incomplete type.
+
+  __builtin_memset(hwparams, 0, 256);  // No crash alignment = 1
+  // CHECK: call void @llvm.memset{{.*}}256, i32 1, i1 false)
+}