diff --git a/mlir/lib/Conversion/StandardToLLVM/StandardToLLVM.cpp b/mlir/lib/Conversion/StandardToLLVM/StandardToLLVM.cpp
--- a/mlir/lib/Conversion/StandardToLLVM/StandardToLLVM.cpp
+++ b/mlir/lib/Conversion/StandardToLLVM/StandardToLLVM.cpp
@@ -3388,7 +3388,7 @@
   SmallVector<LLVM::LLVMType, 8> resultTypes;
   resultTypes.reserve(types.size());
   for (auto t : types) {
-    auto converted = convertType(t).dyn_cast<LLVM::LLVMType>();
+    auto converted = convertType(t).dyn_cast_or_null<LLVM::LLVMType>();
     if (!converted)
       return {};
     resultTypes.push_back(converted);
diff --git a/mlir/test/Conversion/StandardToLLVM/invalid.mlir b/mlir/test/Conversion/StandardToLLVM/invalid.mlir
--- a/mlir/test/Conversion/StandardToLLVM/invalid.mlir
+++ b/mlir/test/Conversion/StandardToLLVM/invalid.mlir
@@ -29,3 +29,7 @@
   %1 = llvm.mlir.cast %0 : vector<1x1xf32> to !llvm.vec<1 x float>
   return %1 : !llvm.vec<1 x float>
 }
+
+// -----
+
+func @partially_supported_signature() -> (vector<10 x i32>, tensor<10 x i32>)