diff --git a/components/coap/Makefile.projbuild b/components/coap/Makefile.projbuild
index e976ee32f..e900b0f9a 100644
--- a/components/coap/Makefile.projbuild
+++ b/components/coap/Makefile.projbuild
@@ -1 +1 @@
-CFLAGS += -DWITH_POSIX
+CPPFLAGS += -DWITH_POSIX
diff --git a/components/mbedtls/Makefile.projbuild b/components/mbedtls/Makefile.projbuild
index 51300efd1..ec9d6f2ce 100644
--- a/components/mbedtls/Makefile.projbuild
+++ b/components/mbedtls/Makefile.projbuild
@@ -1,4 +1,4 @@
 # Anyone compiling mbedTLS code needs the name of the
 # alternative config file
-CFLAGS += -DMBEDTLS_CONFIG_FILE='"mbedtls/esp_config.h"'
+CPPFLAGS += -DMBEDTLS_CONFIG_FILE='"mbedtls/esp_config.h"'
 
diff --git a/components/nghttp/Makefile.projbuild b/components/nghttp/Makefile.projbuild
index 5c6ce7fc9..d17beccad 100644
--- a/components/nghttp/Makefile.projbuild
+++ b/components/nghttp/Makefile.projbuild
@@ -1 +1 @@
-CFLAGS += -DHAVE_CONFIG_H
+CPPFLAGS += -DHAVE_CONFIG_H