diff --git a/c/main.c b/c/main.c
index 6d4c0e0..f002d9b 100644
--- a/c/main.c
+++ b/c/main.c
@@ -9,8 +9,8 @@
 ** the top. -Olin
 */
 #if !defined(DEFAULT_HEAP_SIZE)
-/* 4 megacell = 16 megabytes (8 meg per semispace) */
-#define DEFAULT_HEAP_SIZE 4500000L
+/* 5 megacell = 20 megabytes (10 meg per semispace) */
+#define DEFAULT_HEAP_SIZE 5000000L
 #endif
 
 #if !defined(DEFAULT_STACK_SIZE)