diff --git a/base/applications/network/telnet/CMakeLists.txt b/base/applications/network/telnet/CMakeLists.txt
index 8d0de5ac306..a11ea4f3628 100644
--- a/base/applications/network/telnet/CMakeLists.txt
+++ b/base/applications/network/telnet/CMakeLists.txt
@@ -36,7 +36,10 @@ if (NOT MSVC)
 endif()
 
 if(CMAKE_C_COMPILER_ID STREQUAL "GNU" OR CMAKE_C_COMPILER_ID STREQUAL "Clang")
-    target_compile_options(telnet PRIVATE -Wno-restrict $<$<COMPILE_LANGUAGE:CXX>:-Wno-narrowing>)
+    target_compile_options(telnet PRIVATE $<$<COMPILE_LANGUAGE:CXX>:-Wno-narrowing>)
+    if(CMAKE_C_COMPILER_ID STREQUAL "GNU")
+        target_compile_options(telnet PRIVATE $<$<COMPILE_LANGUAGE:CXX>:-Wno-restrict>)
+    endif()
 endif()
 
 set_module_type(telnet win32cui)
diff --git a/drivers/filesystems/udfs/Include/mem_tools.h b/drivers/filesystems/udfs/Include/mem_tools.h
index fdc29f2a1a7..d05cc9b2c23 100644
--- a/drivers/filesystems/udfs/Include/mem_tools.h
+++ b/drivers/filesystems/udfs/Include/mem_tools.h
@@ -222,7 +222,7 @@ VOID inline MyFreePool__(PVOID addr) {
 #endif //MY_MEM_BOUNDS_CHECK
 
 /* This function just scares the hell out of GCC */
-#ifdef __GNUC__
+#if defined(__GNUC__) && !defined(__clang__)
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wstringop-overflow"
 #endif
@@ -298,7 +298,7 @@ ULONG inline MyReallocPool__(PCHAR addr, ULONG len, PCHAR *pnewaddr, ULONG newle
 */
     return newlen;
 }
-#ifdef __GNUC__
+#if defined(__GNUC__) && !defined(__clang__)
 #pragma GCC diagnostic pop
 #endif
 
diff --git a/modules/rosapps/applications/devutils/createspec/CMakeLists.txt b/modules/rosapps/applications/devutils/createspec/CMakeLists.txt
index e008438e191..f483aa07fee 100644
--- a/modules/rosapps/applications/devutils/createspec/CMakeLists.txt
+++ b/modules/rosapps/applications/devutils/createspec/CMakeLists.txt
@@ -2,8 +2,8 @@
 add_executable(createspec createspec.c)
 set_module_type(createspec win32cui)
 target_link_libraries(createspec wine)
-if(NOT MSVC)
-    target_compile_options(createspec PRIVATE -Wno-stringop-overflow)
+if(CMAKE_C_COMPILER_ID STREQUAL "GNU")
+    target_compile_options(createspec PRIVATE $<$<COMPILE_LANGUAGE:C>:-Wno-stringop-overflow>)
 endif()
 add_importlibs(createspec dbghelp msvcrt kernel32)
 add_cd_file(TARGET createspec DESTINATION reactos/system32 FOR all)
diff --git a/modules/rostests/winetests/msvcrt/CMakeLists.txt b/modules/rostests/winetests/msvcrt/CMakeLists.txt
index 40e532ab653..53cb3a0067c 100644
--- a/modules/rostests/winetests/msvcrt/CMakeLists.txt
+++ b/modules/rostests/winetests/msvcrt/CMakeLists.txt
@@ -28,7 +28,10 @@ target_compile_definitions(msvcrt_winetest PRIVATE
     __msvcrt_ulong=ULONG)
 
 if(CMAKE_C_COMPILER_ID STREQUAL "GNU" OR CMAKE_C_COMPILER_ID STREQUAL "Clang")
-    target_compile_options(msvcrt_winetest PRIVATE -Wno-format -Wno-stringop-truncation -Wno-overflow)
+    target_compile_options(msvcrt_winetest PRIVATE $<$<COMPILE_LANGUAGE:C>:-Wno-format -Wno-overflow>)
+    if(CMAKE_C_COMPILER_ID STREQUAL "GNU")
+        target_compile_options(msvcrt_winetest PRIVATE $<$<COMPILE_LANGUAGE:C>:-Wno-stringop-truncation>)
+    endif()
 endif()
 
 set_module_type(msvcrt_winetest win32cui)
diff --git a/sdk/cmake/gcc.cmake b/sdk/cmake/gcc.cmake
index 384aec75e8d..0acd34cc8c9 100644
--- a/sdk/cmake/gcc.cmake
+++ b/sdk/cmake/gcc.cmake
@@ -96,6 +96,10 @@ add_compile_options(-march=${OARCH} -mtune=${TUNE})
 # Warnings, errors
 if((NOT CMAKE_BUILD_TYPE STREQUAL "Release") AND (NOT CMAKE_C_COMPILER_ID STREQUAL Clang))
     add_compile_options(-Werror)
+else()
+    if(CMAKE_C_COMPILER_ID STREQUAL "Clang")
+        add_compile_options($<$<COMPILE_LANGUAGE:C,CXX>:-Werror=unknown-warning-option>)
+    endif()
 endif()
 
 add_compile_options(-Wall -Wpointer-arith)
diff --git a/sdk/cmake/msvc.cmake b/sdk/cmake/msvc.cmake
index be080bf40dd..24f59b2d833 100644
--- a/sdk/cmake/msvc.cmake
+++ b/sdk/cmake/msvc.cmake
@@ -23,8 +23,7 @@ endif()
 add_compile_options(/GF)
 
 # Enable function level linking and comdat folding (only C/C++, not ASM!)
-add_compile_options($<$<COMPILE_LANGUAGE:CXX>:/Gy>)
-add_compile_options($<$<COMPILE_LANGUAGE:C>:/Gy>)
+add_compile_options($<$<COMPILE_LANGUAGE:C,CXX>:/Gy>)
 add_link_options(/OPT:REF /OPT:ICF)
 
 if(ARCH STREQUAL "i386")
@@ -145,6 +144,7 @@ endif()
 add_compile_options(/w14115)
 
 if(CMAKE_C_COMPILER_ID STREQUAL "Clang")
+    add_compile_options($<$<COMPILE_LANGUAGE:C,CXX>:-Werror=unknown-warning-option>)
     add_compile_options("$<$<COMPILE_LANGUAGE:C,CXX>:-nostdinc;-Wno-multichar;-Wno-char-subscripts;-Wno-microsoft-enum-forward-reference;-Wno-pragma-pack;-Wno-microsoft-anon-tag;-Wno-parentheses-equality;-Wno-unknown-pragmas>")
 endif()