diff --git a/openbsc/configure.ac b/openbsc/configure.ac
index 5cd5d2d..0980413 100644
--- a/openbsc/configure.ac
+++ b/openbsc/configure.ac
@@ -63,7 +63,7 @@
 AC_ARG_WITH([g729], [AS_HELP_STRING([--with-g729], [Enable G.729 encoding/decoding.])], [osmo_ac_with_g729="$withval"],[osmo_ac_with_g729="no"])
 
 if test "$osmo_ac_mgcp_transcoding" = "yes" ; then
-    AC_SEARCH_LIBS([gsm_create], [gsm], [LIBRARY_GSM="$LIBS";LIBS=""])
+    AC_SEARCH_LIBS([gsm_create], [gsm], [LIBRARY_GSM="$LIBS";LIBS=""], [AC_MSG_ERROR([--enable-mgcp-transcoding: cannot find usable libgsm])])
     AC_SUBST(LIBRARY_GSM)
     if test "$osmo_ac_with_g729" = "yes" ; then
 	PKG_CHECK_MODULES(LIBBCG729, libbcg729 >= 0.1, [AC_DEFINE([HAVE_BCG729], [1], [Use bgc729 decoder/encoder])])