diff --git a/src/ncp/Makefile.am b/src/ncp/Makefile.am
index 1c335af7d..fa7209869 100644
--- a/src/ncp/Makefile.am
+++ b/src/ncp/Makefile.am
@@ -50,24 +50,14 @@ COMMON_CPPFLAGS                                   = \
     $(OPENTHREAD_TARGET_DEFINES)                    \
     $(NULL)
 
-
-COMMON_CXXFLAGS                                   = \
-    -I$(top_srcdir)/include                         \
-    -I$(top_srcdir)/src                             \
-    -I$(top_srcdir)/src/core                        \
-    -I$(top_srcdir)/third_party                     \
-    -D_GNU_SOURCE                                   \
-    $(OPENTHREAD_TARGET_DEFINES)                    \
-    $(NULL)
-
 libopenthread_ncp_mtd_a_CPPFLAGS                  = \
     -DOPENTHREAD_MTD=1                              \
-    $(COMMON_CXXFLAGS)                              \
+    $(COMMON_CPPFLAGS)                              \
     $(NULL)
 
 libopenthread_ncp_ftd_a_CPPFLAGS                  = \
     -DOPENTHREAD_FTD=1                              \
-    $(COMMON_CXXFLAGS)                              \
+    $(COMMON_CPPFLAGS)                              \
     $(NULL)
 
 COMMON_SOURCES                                    = \
@@ -101,7 +91,7 @@ if OPENTHREAD_BUILD_TESTS
 
 noinst_PROGRAMS                                   = spinel-test
 spinel_test_SOURCES                               = spinel.c
-spinel_test_CFLAGS                                = -DSPINEL_SELF_TEST=1 -D_GNU_SOURCE -I$(top_srcdir)/src/core
+spinel_test_CFLAGS                                = -DSPINEL_SELF_TEST=1 $(COMMON_CPPFLAGS)
 
 TESTS                                             = spinel-test
 
diff --git a/src/ncp/spinel.c b/src/ncp/spinel.c
index 7fea3ff2f..4ef86f3e6 100644
--- a/src/ncp/spinel.c
+++ b/src/ncp/spinel.c
@@ -1892,10 +1892,6 @@ const char *spinel_capability_to_cstr(unsigned int capability)
 
 #if SPINEL_SELF_TEST
 
-#include <stdlib.h>
-#include "utils/wrap_string.h"
-
-
 int
 main(void)
 {