diff --git a/.unreleased/bugfix_5786 b/.unreleased/bugfix_5786
new file mode 100644
index 00000000000..ef4bf1b49a3
--- /dev/null
+++ b/.unreleased/bugfix_5786
@@ -0,0 +1 @@
+Fixes: #5786 Ensure pg_config --cppflags are passed
\ No newline at end of file
diff --git a/src/build-defs.cmake b/src/build-defs.cmake
index 041d6d8b362..47c2ba7e3c2 100644
--- a/src/build-defs.cmake
+++ b/src/build-defs.cmake
@@ -7,8 +7,7 @@ if(UNIX)
   set(CMAKE_C_STANDARD 11)
   set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -L${PG_LIBDIR}")
   set(CMAKE_MODULE_LINKER_FLAGS "${CMAKE_MODULE_LINKER_FLAGS} -L${PG_LIBDIR}")
-  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${PG_CFLAGS}")
-  set(CMAKE_CPP_FLAGS "${CMAKE_CPP_FLAGS} ${PG_CPPFLAGS}")
+  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${PG_CFLAGS} ${PG_CPPFLAGS}")
   set(CMAKE_C_FLAGS_DEBUG "${CMAKE_C_FLAGS_DEBUG} -g")
 endif()
 
diff --git a/tsl/src/build-defs.cmake b/tsl/src/build-defs.cmake
index 1b5144ae924..c490a4b060d 100644
--- a/tsl/src/build-defs.cmake
+++ b/tsl/src/build-defs.cmake
@@ -5,8 +5,7 @@ if(UNIX)
   set(CMAKE_C_STANDARD 11)
   set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -L${PG_LIBDIR}")
   set(CMAKE_MODULE_LINKER_FLAGS "${CMAKE_MODULE_LINKER_FLAGS} -L${PG_LIBDIR}")
-  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${PG_CFLAGS}")
-  set(CMAKE_CPP_FLAGS "${CMAKE_CPP_FLAGS} ${PG_CPPFLAGS}")
+  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${PG_CFLAGS} ${PG_CPPFLAGS}")
   set(CMAKE_C_FLAGS_DEBUG "${CMAKE_C_FLAGS_DEBUG} -g")
 endif()