diff --git a/javascript/extractor/src/com/semmle/js/parser/JSONParser.java b/javascript/extractor/src/com/semmle/js/parser/JSONParser.java
index fb2c06e82bc..26af68b0cd3 100644
--- a/javascript/extractor/src/com/semmle/js/parser/JSONParser.java
+++ b/javascript/extractor/src/com/semmle/js/parser/JSONParser.java
@@ -79,7 +79,7 @@ public class JSONParser {
   }
 
   private char peek() {
-    return offset < length ? src.charAt(offset) : (char) -1;
+    return offset < length ? src.charAt(offset) : Character.MAX_VALUE;
   }
 
   private JSONValue readValue() throws ParseError {
@@ -356,7 +356,7 @@ public class JSONParser {
     char c;
     next();
     next();
-    while ((c = peek()) != '\r' && c != '\n') next();
+    while ((c = peek()) != '\r' && c != '\n' && c != Character.MAX_VALUE) next();
   }
 
   /** Skips the block comment starting at the current position. */
@@ -367,6 +367,7 @@ public class JSONParser {
     next();
     do {
       c = peek();
+      if (c == Character.MAX_VALUE) raise("Unterminated comment");
       next();
       if (c == '*' && peek() == '/') {
         next();