diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/ArtifactFunction.java b/src/main/java/com/google/devtools/build/lib/skyframe/ArtifactFunction.java
index 8a24daf..f6d728e 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/ArtifactFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/ArtifactFunction.java
@@ -368,7 +368,7 @@
         case CANNOT_CROSS_PACKAGE_BOUNDARY:
           throw new IllegalStateException(
               String.format(
-                  "Package boundary mode was cross: %s %s %s" + artifact, fileValue, request),
+                  "Package boundary mode was cross: %s %s %s", artifact, fileValue, request),
               e);
         case GENERATED_PATH_CONFLICT:
           throw new IllegalStateException(