diff --git a/ax_init_standard_project.m4 b/ax_init_standard_project.m4
index 92ae822..d27f299 100644
--- a/ax_init_standard_project.m4
+++ b/ax_init_standard_project.m4
@@ -364,10 +364,10 @@ AC_DEFUN([AX_PKG_REQUIRE], [
       done
       if test ${$1_found} -eq 0; then
         for p in /usr/include ${$1_CFLAGS}; do
-          $1_file=${p#-I}/$(find ${p#-I} -name $3)
+          $1_file=$(find ${p\#-I} -name $3)
           if test -e ${$1_file}; then
             AC_MSG_WARN([Header file $3 found in ${$1_file%/$3}])
-            $1_CFLAGS="${$1_CFLAGS} -I${p#-I}/${$1_file%/$3}"
+            $1_CFLAGS="${$1_CFLAGS} -I${p\#-I}/${$1_file%/$3}"
             $1_found=1
             break
           fi