diff --git a/old-configure.in b/old-configure.in
index ce29bb0034..4a527b4e20 100644
--- a/old-configure.in
+++ b/old-configure.in
@@ -5572,7 +5572,7 @@ ac_configure_args="$_SUBDIR_CONFIG_ARGS"
 
 # --with-system-nspr will have been converted into the relevant $NSPR_CFLAGS
 # and $NSPR_LIBS.
-ac_configure_args="`echo $ac_configure_args | sed -e 's/--with-system-nspr\S* *//'`"
+ac_configure_args="`echo $ac_configure_args | sed -e 's/--with-system-nspr[^[:space:]]* *//'`"
 
 if test -n "$NSPR_CFLAGS" -o -n "$NSPR_LIBS"; then
     ac_configure_args="$ac_configure_args --with-nspr-cflags='$NSPR_CFLAGS'"