diff --git a/bin/rivet-cmphistos b/bin/rivet-cmphistos
--- a/bin/rivet-cmphistos
+++ b/bin/rivet-cmphistos
@@ -371,7 +371,7 @@ if __name__ == '__main__':
         #     plot[key] = val
         if plotoptions.has_key("PLOT"):
             for key_val in plotoptions["PLOT"]:
-                key, val = [s.strip() for s in key_val.split("=")]
+                key, val = [s.strip() for s in key_val.split("=", 1)]
                 plot[key] = val
         if opts.LINEAR:
             plot['LogY'] = '0'