diff --git a/config/llvm.m4 b/config/llvm.m4
index c6cf8858f64..7a3fff50638 100644
--- a/config/llvm.m4
+++ b/config/llvm.m4
@@ -4,7 +4,7 @@
 # -----------------
 #
 # Look for the LLVM installation, check that it's new enough, set the
-# corresponding LLVM_{CFLAGS,CXXFLAGS,BINPATH} and LDFLAGS
+# corresponding LLVM_{CFLAGS,CXXFLAGS,BINPATH,LIBS}
 # variables. Also verify that CLANG is available, to transform C
 # into bitcode.
 #
@@ -55,7 +55,7 @@ AC_DEFUN([PGAC_LLVM_SUPPORT],
 
   for pgac_option in `$LLVM_CONFIG --ldflags`; do
     case $pgac_option in
-      -L*) LDFLAGS="$LDFLAGS $pgac_option";;
+      -L*) LLVM_LIBS="$LLVM_LIBS $pgac_option";;
     esac
   done
 
diff --git a/configure b/configure
index 49294304b2b..5c1b20ae467 100755
--- a/configure
+++ b/configure
@@ -5213,7 +5213,7 @@ fi
 
   for pgac_option in `$LLVM_CONFIG --ldflags`; do
     case $pgac_option in
-      -L*) LDFLAGS="$LDFLAGS $pgac_option";;
+      -L*) LLVM_LIBS="$LLVM_LIBS $pgac_option";;
     esac
   done
 
@@ -9020,12 +9020,12 @@ fi
   # Note the user could also set XML2_CFLAGS/XML2_LIBS directly
   for pgac_option in $XML2_CFLAGS; do
     case $pgac_option in
-      -I*|-D*) CPPFLAGS="$CPPFLAGS $pgac_option";;
+      -I*|-D*) INCLUDES="$INCLUDES $pgac_option";;
     esac
   done
   for pgac_option in $XML2_LIBS; do
     case $pgac_option in
-      -L*) LDFLAGS="$LDFLAGS $pgac_option";;
+      -L*) LIBDIRS="$LIBDIRS $pgac_option";;
     esac
   done
 fi
@@ -9250,12 +9250,12 @@ fi
   # note that -llz4 will be added by AC_CHECK_LIB below.
   for pgac_option in $LZ4_CFLAGS; do
     case $pgac_option in
-      -I*|-D*) CPPFLAGS="$CPPFLAGS $pgac_option";;
+      -I*|-D*) INCLUDES="$INCLUDES $pgac_option";;
     esac
   done
   for pgac_option in $LZ4_LIBS; do
     case $pgac_option in
-      -L*) LDFLAGS="$LDFLAGS $pgac_option";;
+      -L*) LIBDIRS="$LIBDIRS $pgac_option";;
     esac
   done
 fi
@@ -9391,12 +9391,12 @@ fi
   # note that -lzstd will be added by AC_CHECK_LIB below.
   for pgac_option in $ZSTD_CFLAGS; do
     case $pgac_option in
-      -I*|-D*) CPPFLAGS="$CPPFLAGS $pgac_option";;
+      -I*|-D*) INCLUDES="$INCLUDES $pgac_option";;
     esac
   done
   for pgac_option in $ZSTD_LIBS; do
     case $pgac_option in
-      -L*) LDFLAGS="$LDFLAGS $pgac_option";;
+      -L*) LIBDIRS="$LIBDIRS $pgac_option";;
     esac
   done
 fi
@@ -16256,7 +16256,7 @@ fi
 
 if test "$with_icu" = yes; then
   ac_save_CPPFLAGS=$CPPFLAGS
-  CPPFLAGS="$ICU_CFLAGS $CPPFLAGS"
+  CPPFLAGS="$CPPFLAGS $ICU_CFLAGS"
 
   # Verify we have ICU's header files
   ac_fn_c_check_header_mongrel "$LINENO" "unicode/ucol.h" "ac_cv_header_unicode_ucol_h" "$ac_includes_default"
@@ -18693,7 +18693,7 @@ Use --without-tcl to disable building PL/Tcl." "$LINENO" 5
     fi
     # now that we have TCL_INCLUDE_SPEC, we can check for <tcl.h>
     ac_save_CPPFLAGS=$CPPFLAGS
-    CPPFLAGS="$TCL_INCLUDE_SPEC $CPPFLAGS"
+    CPPFLAGS="$CPPFLAGS $TCL_INCLUDE_SPEC"
     ac_fn_c_check_header_mongrel "$LINENO" "tcl.h" "ac_cv_header_tcl_h" "$ac_includes_default"
 if test "x$ac_cv_header_tcl_h" = xyes; then :
 
@@ -18762,7 +18762,7 @@ fi
 # check for <Python.h>
 if test "$with_python" = yes; then
   ac_save_CPPFLAGS=$CPPFLAGS
-  CPPFLAGS="$python_includespec $CPPFLAGS"
+  CPPFLAGS="$CPPFLAGS $python_includespec"
   ac_fn_c_check_header_mongrel "$LINENO" "Python.h" "ac_cv_header_Python_h" "$ac_includes_default"
 if test "x$ac_cv_header_Python_h" = xyes; then :
 
diff --git a/configure.ac b/configure.ac
index 3a8da4476d1..ac4ca163a75 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1044,12 +1044,12 @@ if test "$with_libxml" = yes ; then
   # Note the user could also set XML2_CFLAGS/XML2_LIBS directly
   for pgac_option in $XML2_CFLAGS; do
     case $pgac_option in
-      -I*|-D*) CPPFLAGS="$CPPFLAGS $pgac_option";;
+      -I*|-D*) INCLUDES="$INCLUDES $pgac_option";;
     esac
   done
   for pgac_option in $XML2_LIBS; do
     case $pgac_option in
-      -L*) LDFLAGS="$LDFLAGS $pgac_option";;
+      -L*) LIBDIRS="$LIBDIRS $pgac_option";;
     esac
   done
 fi
@@ -1093,12 +1093,12 @@ if test "$with_lz4" = yes; then
   # note that -llz4 will be added by AC_CHECK_LIB below.
   for pgac_option in $LZ4_CFLAGS; do
     case $pgac_option in
-      -I*|-D*) CPPFLAGS="$CPPFLAGS $pgac_option";;
+      -I*|-D*) INCLUDES="$INCLUDES $pgac_option";;
     esac
   done
   for pgac_option in $LZ4_LIBS; do
     case $pgac_option in
-      -L*) LDFLAGS="$LDFLAGS $pgac_option";;
+      -L*) LIBDIRS="$LIBDIRS $pgac_option";;
     esac
   done
 fi
@@ -1118,12 +1118,12 @@ if test "$with_zstd" = yes; then
   # note that -lzstd will be added by AC_CHECK_LIB below.
   for pgac_option in $ZSTD_CFLAGS; do
     case $pgac_option in
-      -I*|-D*) CPPFLAGS="$CPPFLAGS $pgac_option";;
+      -I*|-D*) INCLUDES="$INCLUDES $pgac_option";;
     esac
   done
   for pgac_option in $ZSTD_LIBS; do
     case $pgac_option in
-      -L*) LDFLAGS="$LDFLAGS $pgac_option";;
+      -L*) LIBDIRS="$LIBDIRS $pgac_option";;
     esac
   done
 fi
@@ -1901,7 +1901,7 @@ fi
 
 if test "$with_icu" = yes; then
   ac_save_CPPFLAGS=$CPPFLAGS
-  CPPFLAGS="$ICU_CFLAGS $CPPFLAGS"
+  CPPFLAGS="$CPPFLAGS $ICU_CFLAGS"
 
   # Verify we have ICU's header files
   AC_CHECK_HEADER(unicode/ucol.h, [],
@@ -2331,7 +2331,7 @@ Use --without-tcl to disable building PL/Tcl.])
     fi
     # now that we have TCL_INCLUDE_SPEC, we can check for <tcl.h>
     ac_save_CPPFLAGS=$CPPFLAGS
-    CPPFLAGS="$TCL_INCLUDE_SPEC $CPPFLAGS"
+    CPPFLAGS="$CPPFLAGS $TCL_INCLUDE_SPEC"
     AC_CHECK_HEADER(tcl.h, [], [AC_MSG_ERROR([header file <tcl.h> is required for Tcl])])
     CPPFLAGS=$ac_save_CPPFLAGS
 fi
@@ -2368,7 +2368,7 @@ fi
 # check for <Python.h>
 if test "$with_python" = yes; then
   ac_save_CPPFLAGS=$CPPFLAGS
-  CPPFLAGS="$python_includespec $CPPFLAGS"
+  CPPFLAGS="$CPPFLAGS $python_includespec"
   AC_CHECK_HEADER(Python.h, [], [AC_MSG_ERROR([header file <Python.h> is required for Python])])
   CPPFLAGS=$ac_save_CPPFLAGS
 fi
diff --git a/src/Makefile.global.in b/src/Makefile.global.in
index a00c909681e..0c6c31b5bee 100644
--- a/src/Makefile.global.in
+++ b/src/Makefile.global.in
@@ -240,7 +240,7 @@ CPP = @CPP@
 CPPFLAGS = @CPPFLAGS@
 PG_SYSROOT = @PG_SYSROOT@
 
-override CPPFLAGS := $(ICU_CFLAGS) $(CPPFLAGS)
+override CPPFLAGS += $(ICU_CFLAGS)
 
 ifdef PGXS
 override CPPFLAGS := -I$(includedir_server) -I$(includedir_internal) $(CPPFLAGS)
diff --git a/src/backend/jit/llvm/Makefile b/src/backend/jit/llvm/Makefile
index e9fd195cc22..10c7d719902 100644
--- a/src/backend/jit/llvm/Makefile
+++ b/src/backend/jit/llvm/Makefile
@@ -31,7 +31,7 @@ endif
 # All files in this directory use LLVM.
 CFLAGS += $(LLVM_CFLAGS)
 CXXFLAGS += $(LLVM_CXXFLAGS)
-override CPPFLAGS := $(LLVM_CPPFLAGS) $(CPPFLAGS)
+override CPPFLAGS += $(LLVM_CPPFLAGS)
 SHLIB_LINK += $(LLVM_LIBS)
 
 # Because this module includes C++ files, we need to use a C++
diff --git a/src/bin/initdb/Makefile b/src/bin/initdb/Makefile
index 031cc77c9d6..adc9940d64c 100644
--- a/src/bin/initdb/Makefile
+++ b/src/bin/initdb/Makefile
@@ -20,7 +20,7 @@ include $(top_builddir)/src/Makefile.global
 # from libpq, else we have risks of version skew if we run with a libpq
 # shared library from a different PG version.  Define
 # USE_PRIVATE_ENCODING_FUNCS to ensure that that happens.
-override CPPFLAGS := -DUSE_PRIVATE_ENCODING_FUNCS -I$(libpq_srcdir) -I$(top_srcdir)/src/timezone $(ICU_CFLAGS) $(CPPFLAGS)
+override CPPFLAGS := -DUSE_PRIVATE_ENCODING_FUNCS -I$(libpq_srcdir) -I$(top_srcdir)/src/timezone $(CPPFLAGS) $(ICU_CFLAGS)
 
 # We need libpq only because fe_utils does.
 LDFLAGS_INTERNAL += -L$(top_builddir)/src/fe_utils -lpgfeutils $(libpq_pgport) $(ICU_LIBS)
diff --git a/src/interfaces/libpq/Makefile b/src/interfaces/libpq/Makefile
index b36a7657648..e4206ac8540 100644
--- a/src/interfaces/libpq/Makefile
+++ b/src/interfaces/libpq/Makefile
@@ -22,7 +22,7 @@ NAME= pq
 SO_MAJOR_VERSION= 5
 SO_MINOR_VERSION= $(MAJORVERSION)
 
-override CPPFLAGS :=  -I$(srcdir) $(CPPFLAGS) -I$(top_builddir)/src/port -I$(top_srcdir)/src/port
+override CPPFLAGS := -I$(srcdir) -I$(top_builddir)/src/port -I$(top_srcdir)/src/port $(CPPFLAGS)
 ifneq ($(PORTNAME), win32)
 override CFLAGS += $(PTHREAD_CFLAGS)
 endif
diff --git a/src/pl/plpython/Makefile b/src/pl/plpython/Makefile
index f959083a0bd..25f295c3709 100644
--- a/src/pl/plpython/Makefile
+++ b/src/pl/plpython/Makefile
@@ -11,7 +11,7 @@ ifeq ($(PORTNAME), win32)
 override python_libspec =
 endif
 
-override CPPFLAGS := -I. -I$(srcdir) $(python_includespec) $(CPPFLAGS)
+override CPPFLAGS := -I. -I$(srcdir) $(CPPFLAGS) $(python_includespec)
 
 rpathdir = $(python_libdir)
 
diff --git a/src/pl/tcl/Makefile b/src/pl/tcl/Makefile
index ea52a2efc22..dd57f7d694c 100644
--- a/src/pl/tcl/Makefile
+++ b/src/pl/tcl/Makefile
@@ -11,7 +11,7 @@ top_builddir = ../../..
 include $(top_builddir)/src/Makefile.global
 
 
-override CPPFLAGS := -I. -I$(srcdir) $(TCL_INCLUDE_SPEC) $(CPPFLAGS)
+override CPPFLAGS := -I. -I$(srcdir) $(CPPFLAGS) $(TCL_INCLUDE_SPEC)
 
 # On Windows, we don't link directly with the Tcl library; see below
 ifneq ($(PORTNAME), win32)