diff --git a/src/number.c b/src/number.c
index 962a2c3f..1f2e2b9e 100644
--- a/src/number.c
+++ b/src/number.c
@@ -198,7 +198,7 @@ pic_number_atan(pic_state *pic)
   double f,g;
   int argc;
 
-  argc = pic_get_args(pic, "f|g", &f, &g);
+  argc = pic_get_args(pic, "f|f", &f, &g);
   if (argc == 1) {
     f = atan(f);
     return pic_float_value(f);
diff --git a/src/vm.c b/src/vm.c
index 4a185ea3..82d02516 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -74,6 +74,10 @@ pic_get_args(pic_state *pic, const char *format, ...)
 	}
       }
       break;
+    default:
+      {
+	pic_error(pic, "pic_get_args: invalid argument specifier given");
+      }
     }
   }
   if (argc > i) {