diff --git a/git-gui.sh b/git-gui.sh
index daee5601b1..cc1625bfac 100755
--- a/git-gui.sh
+++ b/git-gui.sh
@@ -20,6 +20,22 @@ You should have received a copy of the GNU General Public License
 along with this program; if not, write to the Free Software
 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA}
 
+######################################################################
+##
+## Tcl/Tk sanity check
+
+if {[catch {package require Tcl 8.4} err]
+ || [catch {package require Tk  8.4} err]
+} {
+	catch {wm withdraw .}
+	tk_messageBox \
+		-icon error \
+		-type ok \
+		-title "git-gui: fatal error" \
+		-message $err
+	exit 1
+}
+
 ######################################################################
 ##
 ## configure our library