diff --git a/cmake/ncnn_add_layer.cmake b/cmake/ncnn_add_layer.cmake
index d9f898f62c9..50d7dcf89ce 100644
--- a/cmake/ncnn_add_layer.cmake
+++ b/cmake/ncnn_add_layer.cmake
@@ -345,7 +345,8 @@ macro(ncnn_add_layer class)
                 ncnn_add_arch_opt_source(${class} asimddp "-march=armv8.2-a+fp16+dotprod")
             endif()
             if(NCNN_RUNTIME_CPU AND NCNN_ARM82FP16FML)
-                ncnn_add_arch_opt_source(${class} asimdfhm "-march=armv8.2-a+fp16+fp16fml")
+                # clang 9.0.9 shipped with android ndk-r21 is missing __ARM_FEATURE_FP16_FML macro for asimdfhm target
+                ncnn_add_arch_opt_source(${class} asimdfhm "-march=armv8.2-a+fp16+fp16fml -D__ARM_FEATURE_FP16_FML")
             endif()
             if(NCNN_RUNTIME_CPU AND NCNN_ARM84BF16)
                 ncnn_add_arch_opt_source(${class} bf16 "-march=armv8.4-a+fp16+dotprod+bf16")
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 21d5ae5eae3..b27f8ad42bd 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -634,6 +634,8 @@ if(NCNN_TARGET_ARCH STREQUAL "arm" AND (CMAKE_SIZEOF_VOID_P EQUAL 8 OR NCNN_TARG
             endif()
             if(NCNN_ARM82FP16FML)
                 set(ARM_MARCH_FLAG "${ARM_MARCH_FLAG}+fp16fml")
+                # clang 9.0.9 shipped with android ndk-r21 is missing __ARM_FEATURE_FP16_FML macro for asimdfhm target
+                target_compile_options(ncnn PRIVATE -D__ARM_FEATURE_FP16_FML)
             endif()
         endif()
     endif()