diff --git a/gen/functions.cpp b/gen/functions.cpp
index f3bf2571..96b58fca 100644
--- a/gen/functions.cpp
+++ b/gen/functions.cpp
@@ -612,7 +612,16 @@ static void set_param_attrs(TypeFunction* f, llvm::Function* func, FuncDeclarati
     llvm::AttrListPtr oldAttrs = func->getAttributes();
 #endif
     for (size_t i = 0; i < oldAttrs.getNumSlots(); ++i) {
+#if LDC_LLVM_VER >= 303
+        const unsigned Index = oldAttrs.getSlotIndex(i);
+        llvm::AttrBuilder &builder = llvm::AttrBuilder(oldAttrs.getSlotAttributes(i), Index).addAttribute(llvm::Attribute::None);
+        llvm::AttributeWithIndex curr = llvm::AttributeWithIndex::get(Index,
+                                                                      llvm::Attribute::get(
+                                                                          gIR->context(),
+                                                                          builder));
+#else
         llvm::AttributeWithIndex curr = oldAttrs.getSlot(i);
+#endif
 
         bool found = false;
         for (size_t j = 0; j < newSize; ++j) {
diff --git a/runtime/CMakeLists.txt b/runtime/CMakeLists.txt
index 12155111..7aee5dcf 100644
--- a/runtime/CMakeLists.txt
+++ b/runtime/CMakeLists.txt
@@ -316,10 +316,12 @@ macro(build_runtime d_flags c_flags ld_flags lib_suffix path_suffix outlist_targ
         dc(${f} "${d_flags}" "${RUNTIME_DIR}" "${target_suffix}" DCRT_O DCRT_BC)
     endforeach()
 
-    # Always build zlib and other C parts of the runtime in release mode.
-    set_source_files_properties(${CORE_C} ${DCRT_C} PROPERTIES
-        COMPILE_FLAGS "${CMAKE_C_FLAGS} ${CMAKE_C_FLAGS_RELEASE}"
-    )
+    if(NOT MSVC)
+        # Always build zlib and other C parts of the runtime in release mode.
+        set_source_files_properties(${CORE_C} ${DCRT_C} PROPERTIES
+            COMPILE_FLAGS "${CMAKE_C_FLAGS} ${CMAKE_C_FLAGS_RELEASE}"
+        )
+    endif()
 
     if(EXISTS ${RUNTIME_DIR})
         set(GCCBUILTINS "${PROJECT_BINARY_DIR}/gccbuiltins_x86.di")