diff --git a/flang/lib/Lower/CMakeLists.txt b/flang/lib/Lower/CMakeLists.txt
--- a/flang/lib/Lower/CMakeLists.txt
+++ b/flang/lib/Lower/CMakeLists.txt
@@ -1,4 +1,6 @@
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-error -Wno-unused-parameter")
+if (LLVM_COMPILER_IS_GCC_COMPATIBLE)
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-error -Wno-unused-parameter")
+endif ()
 get_property(dialect_libs GLOBAL PROPERTY MLIR_DIALECT_LIBS)
 
 add_flang_library(FortranLower
diff --git a/flang/lib/Optimizer/CMakeLists.txt b/flang/lib/Optimizer/CMakeLists.txt
--- a/flang/lib/Optimizer/CMakeLists.txt
+++ b/flang/lib/Optimizer/CMakeLists.txt
@@ -1,4 +1,6 @@
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-unused-parameter -Wno-error")
+if (LLVM_COMPILER_IS_GCC_COMPATIBLE)
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-unused-parameter -Wno-error")
+endif ()
 get_property(dialect_libs GLOBAL PROPERTY MLIR_DIALECT_LIBS)
 
 add_flang_library(FIROptimizer