diff --git a/pegs.c b/pegs.c
index f3f07bb..4cfd4a0 100644
--- a/pegs.c
+++ b/pegs.c
@@ -486,7 +486,9 @@ static void pegs_generate(unsigned char *grid, int w, int h, random_state *rs)
 	printf("insufficient extent; trying again\n");
 #endif
     }
+#ifdef GENERATION_DIAGNOSTICS
     fflush(stdout);
+#endif
 }
 
 /* ----------------------------------------------------------------------