diff --git a/config.make.in b/config.make.in
index eb34cd1d34..dd705ae56f 100644
--- a/config.make.in
+++ b/config.make.in
@@ -4,7 +4,7 @@ topdir := @abs_top_srcdir@/
 builddir := @abs_top_builddir@/
 libdir := ${prefix}/lib/
 installdir := ${prefix}/bin/
-monodir := `pkg-config --variable=libdir mono`/mono/
+monodir := @MONODIR@
 libdir2 := $(monodir)2.0/
 libdir35 := $(monodir)3.5/
 libdir4 := $(monodir)4.0/
diff --git a/configure.ac b/configure.ac
index 2c820d6bba..a25f02e9ac 100644
--- a/configure.ac
+++ b/configure.ac
@@ -21,6 +21,27 @@ AC_ARG_WITH([bootstrap],
 with_bootstrap=$(cd "$with_bootstrap" && pwd)
 AC_SUBST(with_bootstrap)
 
+AC_ARG_WITH([gacdir],
+                    [  --with-gacdir=/path/to/gac      Specify the gac directory (ex: /usr/lib/mono/gac)],
+                [],
+                [with_gacdir=no]
+        )
+
+if test "x$with_gacdir" = "xno"; then
+	MONODIR=`pkg-config --variable=libdir mono`/mono
+	if ! test -e $MONODIR/2.0/mscorlib.dll; then
+		MONODIR=`pkg-config --variable=prefix mono`/lib/mono
+	fi
+else
+	MONODIR=$(cd "$with_gacdir/.." && pwd)
+fi
+
+if ! test -e $MONODIR/2.0/mscorlib.dll; then
+	AC_ERROR(Couldn't find the mono gac directory or mscorlib.dll in the usual places. Set --with-gacdir=<path>)
+fi
+AC_SUBST(MONODIR)
+
+
 AC_CONFIG_FILES([
 launcher
 Makefile