--- a/ustr-conf.h.in	2007-10-22 08:00:55.000000000 +0200
+++ b/ustr-conf.h.in	2015-09-10 12:24:34.998796842 +0200
@@ -4,13 +4,24 @@
 /* this is the custom version for the library itself, for everyone else
  * ustr-import generates one depending on the options. */
 
+/* If this is GCC with major version 5 and up, the default C standard
+ * has changed from C89 to C99 so the old inline behaviour must be
+ * restored:
+ */
+#if defined(__GNUC__) \
+ && (__GNUC__ > 4) \
+ && defined(__STDC_VERSION__) \
+ && (__STDC_VERSION__ >= 199901L)
+#  define inline inline __attribute__ ((gnu_inline))
+#endif /* GCC greater than major version 4 and not -std=c89 set */
+
 /* The default is now to link against libc. */
 #ifndef USTR_CONF_INCLUDE_CODEONLY_HEADERS
 #define USTR_CONF_INCLUDE_CODEONLY_HEADERS 0
 #endif
 
 /* We can't: if defined(__GLIBC__) && (!defined(_GNU_SOURCE) || !_GNU_SOURCE)
- *  because by the time we've included a libc header it's too late. */ 
+ *  because by the time we've included a libc header it's too late. */
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE 1
 #endif