3 files changed, 3 insertions, 3 deletions

diff --git a/aclocal.m4 b/aclocal.m4
index 21fcec9..3884f20 100644
--- a/aclocal.m4
+++ b/aclocal.m4
@@ -69,7 +69,7 @@ AC_DEFUN(ZINC_ENABLE_GL, [
 	    GL_LIBS=-lopengl32
 	else
  	  GL_LIBS="-lGL"
- 	  GL_INCLUDES='/usr/include'
+ 	  GL_INCLUDES='-I/usr/include'
         fi
 
  	AC_DEFINE(GL)
diff --git a/configure b/configure
index 523c699..459b514 100755
--- a/configure
+++ b/configure
@@ -4236,7 +4236,7 @@ fi
 	    GL_LIBS=-lopengl32
 	else
  	  GL_LIBS="-lGL"
- 	  GL_INCLUDES='/usr/include'
+ 	  GL_INCLUDES='-I/usr/include'
         fi
 
  	cat >> confdefs.h <<\EOF
diff --git a/tkzinc.m4 b/tkzinc.m4
index e1fde7e..b18f25f 100644
--- a/tkzinc.m4
+++ b/tkzinc.m4
@@ -56,7 +56,7 @@ AC_DEFUN(ZINC_ENABLE_GL, [
 	    GL_LIBS=-lopengl32
 	else
  	  GL_LIBS="-lGL"
- 	  GL_INCLUDES='/usr/include'
+ 	  GL_INCLUDES='-I/usr/include'
         fi
 
  	AC_DEFINE(GL)