diff --git a/src/main/java/com/google/devtools/build/lib/rules/apple/DottedVersion.java b/src/main/java/com/google/devtools/build/lib/rules/apple/DottedVersion.java
index 4380d96..de5041d 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/apple/DottedVersion.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/apple/DottedVersion.java
@@ -130,7 +130,7 @@
   private static final Pattern COMPONENT_PATTERN =
       Pattern.compile("(\\d+)([a-z0-9]*?)?(\\d+)?", Pattern.CASE_INSENSITIVE);
   private static final String ILLEGAL_VERSION =
-      "Dotted version components must all be of the form \\d+([a-z0-9]*?)?(\\d+)? but got %s";
+      "Dotted version components must all be of the form \\d+([a-z0-9]*?)?(\\d+)? but got '%s'";
   private static final String NO_ALPHA_SEQUENCE = null;
   private static final Component ZERO_COMPONENT = new Component(0, NO_ALPHA_SEQUENCE, 0, "0");