gistfile1.diff

diff --git a/core/src/main/java/org/jruby/util/JarResource.java b/core/src/main/java/org/jruby/util/JarResource.java
index a4d5dfa..98ef0d3 100644
--- a/core/src/main/java/org/jruby/util/JarResource.java
+++ b/core/src/main/java/org/jruby/util/JarResource.java
@@ -24,6 +24,9 @@ abstract class JarResource implements FileResource {
             // since pathname is actually an uri we need to decode any url decoded characters like %20
             // which happens when directory names contain spaces
             sanitized = URLDecoder.decode(sanitized, "UTF-8");
+        } catch (IllegalArgumentException iae) {
+            // not actually a URL, for whatever reason
+            return null;
         } catch (UnsupportedEncodingException e) {
             throw new RuntimeException( "hmm - system does not know UTF-8 string encoding :(" );
         }