diff --git a/literate/Muri.md b/literate/Muri.md
index fe24272..d1049ed 100644
--- a/literate/Muri.md
+++ b/literate/Muri.md
@@ -258,6 +258,10 @@ void pass2(char *fname) {
   buffer = (char *)source;
   here = 0;
   fp = fopen(fname, "r");
+  if (fp == NULL) {
+    printf("Unable to load file\n");
+    exit(2);
+  }
   while (!feof(fp)) {
     read_line(fp, buffer);
     if (strcmp(buffer, "~~~") == 0) {
diff --git a/tools/extend.c b/tools/extend.c
index d8194ae..82118e3 100644
--- a/tools/extend.c
+++ b/tools/extend.c
@@ -332,7 +332,7 @@ void read_token(FILE *file, char *token_buffer, int echo, int max) {
 
 CELL ngaLoadImage(char *imageFile) {
   FILE *fp;
-  CELL imageSize;
+  CELL imageSize = 0;
   long fileLen;
   if ((fp = fopen(imageFile, "rb")) != NULL) {
     /* Determine length (in cells) */
diff --git a/tools/muri.c b/tools/muri.c
index 4a7899a..e9a891c 100644
--- a/tools/muri.c
+++ b/tools/muri.c
@@ -133,6 +133,10 @@ void pass2(char *fname) {
   buffer = (char *)source;
   here = 0;
   fp = fopen(fname, "r");
+  if (fp == NULL) {
+    printf("Unable to load file\n");
+    exit(2);
+  }
   while (!feof(fp)) {
     read_line(fp, buffer);
     if (strcmp(buffer, "~~~") == 0) {