diff --git a/crypto777/OS_nonportable.c b/crypto777/OS_nonportable.c
index 56a7a8258..5537d8441 100755
--- a/crypto777/OS_nonportable.c
+++ b/crypto777/OS_nonportable.c
@@ -600,7 +600,10 @@ void *OS_nonportable_mapfile(char *fname,long *filesizep,int32_t enablewrite)
     if ( ptr == 0 || ptr == MAP_FAILED )
 	{
         if ( enablewrite != 0 )
-            printf("map_file.write%d: mapping %s failed? mp %p\n",enablewrite,fname,ptr);
+        {
+            printf("map_file.write%d: mapping %s failed? mp %p, usually due to ulimit -n exceeded\n",enablewrite,fname,ptr);
+            exit(-1);
+        }
 		return(0);
 	}
 	*filesizep = filesize;
diff --git a/crypto777/OS_portable.c b/crypto777/OS_portable.c
index ff16d4a65..25d74ac03 100755
--- a/crypto777/OS_portable.c
+++ b/crypto777/OS_portable.c
@@ -183,7 +183,8 @@ void *OS_portable_mapfile(char *fname,long *filesizep,int32_t enablewrite)
 	close(fd);
     if ( ptr == 0 || ptr == MAP_FAILED )
 	{
-		printf("map_file.write%d: mapping %s failed? mp %p\n",enablewrite,fname,ptr);
+		printf("map_file.write%d: mapping %s failed? mp %p, usually due to ulimit -n exceeded\n",enablewrite,fname,ptr);
+        exit(-1);
 		return(0);
 	}
 	*filesizep = filesize;