diff --git a/configure.ac b/configure.ac
index 0852e24e2..4986ffe0c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -26,8 +26,7 @@ if test "$user_localdirs" = 1; then
      LDFLAGS="$LDFLAGS -L/usr/local/lib"
      fi
    if test -d /usr/local/include; then
-     CFLAGS="$CFLAGS -I/usr/local/include"
-     CXXFLAGS="$CXXFLAGS -I/usr/local/include"
+     CPPFLAGS="$CPPFLAGS -I/usr/local/include"
    fi
 fi
 
@@ -373,7 +372,7 @@ AC_HELP_STRING([--with-libpcap=included], [Always use version included with Nmap
     have_libpcap=no
    ;;
   *)
-    _cppflags=$CXXFLAGS
+    _cppflags=$CPPFLAGS
     _ldflags=$LDFLAGS
 
     CPPFLAGS="-I$with_libpcap/include $CPPFLAGS"
@@ -386,7 +385,7 @@ AC_HELP_STRING([--with-libpcap=included], [Always use version included with Nmap
 	LIBPCAP_LIB=$with_libpcap/lib])])
 
     LDFLAGS=$_ldflags
-    CXXFLAGS=$_cppflags
+    CPPFLAGS=$_cppflags
     ;;
   esac]
 )
@@ -397,9 +396,6 @@ fi
 
 if test $have_libpcap = yes; then
   if test "${LIBPCAP_INC+set}" = "set"; then
-    _cflags=$CXXFLAGS
-    _ldflags=$LDFLAGS
-
     CPPFLAGS="-I$LIBPCAP_INC $CPPFLAGS"
     LDFLAGS="-L$LIBPCAP_LIB $LDFLAGS"
   fi
diff --git a/nbase/configure.ac b/nbase/configure.ac
index 3b735420f..1442beab3 100644
--- a/nbase/configure.ac
+++ b/nbase/configure.ac
@@ -34,7 +34,7 @@ if test "$user_localdirs" = 1; then
      LDFLAGS="$LDFLAGS -L/usr/local/lib"
      fi
    if test -d /usr/local/include; then
-     CFLAGS="$CFLAGS -I/usr/local/include"
+     CPPFLAGS="$CPPFLAGS -I/usr/local/include"
    fi
 fi
 
diff --git a/ncat/configure.ac b/ncat/configure.ac
index 85f04eeb3..efe650c49 100644
--- a/ncat/configure.ac
+++ b/ncat/configure.ac
@@ -22,7 +22,7 @@ AC_ARG_WITH(openssl,[  --with-openssl=DIR    Use optional openssl libs and inclu
   *)
     specialssldir="$with_openssl"
     LDFLAGS="$LDFLAGS -L$with_openssl/lib"
-    CFLAGS="-I$with_openssl/include $CFLAGS"
+    CPPFLAGS="-I$with_openssl/include $CPPFLAGS"
   ;;
   esac]
 )
diff --git a/nping/configure.ac b/nping/configure.ac
index b6347b10c..598ec3b35 100644
--- a/nping/configure.ac
+++ b/nping/configure.ac
@@ -24,8 +24,7 @@ if test "$user_localdirs" = 1; then
      LDFLAGS="$LDFLAGS -L/usr/local/lib"
      fi
    if test -d /usr/local/include; then
-     CFLAGS="$CFLAGS -I/usr/local/include"
-     CXXFLAGS="$CFLAGS -I/usr/local/include"
+     CPPFLAGS="$CPPFLAGS -I/usr/local/include"
    fi
 fi
 
@@ -203,7 +202,7 @@ AC_HELP_STRING([--with-libpcap=included], [Always use version included with Nmap
     have_libpcap=no
    ;;
   *)
-    _cppflags=$CXXFLAGS
+    _cppflags=$CPPFLAGS
     _ldflags=$LDFLAGS
 
     CPPFLAGS="-I$with_libpcap/include $CPPFLAGS"
@@ -216,7 +215,7 @@ AC_HELP_STRING([--with-libpcap=included], [Always use version included with Nmap
 	LIBPCAP_LIB=$with_libpcap/lib])])
 
     LDFLAGS=$_ldflags
-    CXXFLAGS=$_cppflags
+    CPPFLAGS=$_cppflags
     ;;
   esac]
 )
@@ -227,9 +226,6 @@ fi
 
 if test $have_libpcap = yes; then
   if test "${LIBPCAP_INC+set}" = "set"; then
-    _cflags=$CXXFLAGS
-    _ldflags=$LDFLAGS
-
     CPPFLAGS="-I$LIBPCAP_INC $CPPFLAGS"
     LDFLAGS="-L$LIBPCAP_LIB $LDFLAGS"
   fi