diff --git a/generator/errnostring.ml b/generator/errnostring.ml
index 4a544f337..d16a07ecd 100644
--- a/generator/errnostring.ml
+++ b/generator/errnostring.ml
@@ -231,7 +231,7 @@ extern int guestfs_int_string_to_errno (const char *errnostr);
 
 /* Private structure and function used by the perfect hash implementation. */
 struct errnostring_entry { char *name; int errnum; };
-extern const struct errnostring_entry *guestfs_int_string_to_errno_lookup (register const char *str, register GPERF_SIZE_T len);
+extern const struct errnostring_entry *guestfs_int_string_to_errno_lookup (register const char *str, register unsigned int len);
 
 #endif /* GUESTFS_ERRNOSTRING_H_ */
 "
diff --git a/m4/guestfs_progs.m4 b/m4/guestfs_progs.m4
index 198598cae..c63e62f09 100644
--- a/m4/guestfs_progs.m4
+++ b/m4/guestfs_progs.m4
@@ -50,26 +50,6 @@ AC_CHECK_PROG([GPERF],[gperf],[gperf],[no])
 test "x$GPERF" = "xno" &&
     AC_MSG_ERROR([gperf must be installed])
 
-dnl Determine type of gperf hash function (changed in gperf 3.1).
-AC_MSG_CHECKING([type of gperf hash len parameter])
-cat > conftest.gperf <<EOF
-%language=ANSI-C
-%%
-A, 1
-%%
-EOF
-GPERF_SIZE_T=$(
-    $GPERF conftest.gperf |
-    grep '^hash (.*len)$' |
-    $SED 's/.*, register \([[^,]]*\) len)$/\1/'
-)
-if test "x$GPERF_SIZE_T" = "x"; then
-    AC_MSG_ERROR([could not detect type of gperf hash len parameter])
-fi
-AC_MSG_RESULT([$GPERF_SIZE_T])
-AC_DEFINE_UNQUOTED([GPERF_SIZE_T],[$GPERF_SIZE_T],[Type of gperf hash len parameter.])
-rm conftest.gperf
-
 dnl Check for genisoimage/mkisofs
 AC_PATH_PROGS([GENISOIMAGE],[genisoimage mkisofs],[no],
     [$PATH$PATH_SEPARATOR/usr/sbin$PATH_SEPARATOR/sbin])