diff --git a/configure.ac b/configure.ac
index e6f4982..22077bf 100755
--- a/configure.ac
+++ b/configure.ac
@@ -21,7 +21,8 @@
 AM_INIT_AUTOMAKE(1.6)
 AM_CONFIG_HEADER(config.h)
 
-dnl we need gawk for memtypes.awk
+dnl GNU awk is required for lib/memtype.h made by memtypes.awk.
+dnl BSD awk complains: awk: gensub doesn't support backreferences (subst "\1")
 AC_CHECK_PROG([GAWK],[gawk],[gawk],[/bin/false])
 AC_ARG_VAR([GAWK],[GNU AWK])