diff --git a/imageio/imageio-core/src/main/java/com/twelvemonkeys/imageio/util/IIOInputStreamAdapter.java b/imageio/imageio-core/src/main/java/com/twelvemonkeys/imageio/util/IIOInputStreamAdapter.java
index f9dfea2b..883c828e 100755
--- a/imageio/imageio-core/src/main/java/com/twelvemonkeys/imageio/util/IIOInputStreamAdapter.java
+++ b/imageio/imageio-core/src/main/java/com/twelvemonkeys/imageio/util/IIOInputStreamAdapter.java
@@ -81,7 +81,7 @@ class IIOInputStreamAdapter extends InputStream {
 
     private IIOInputStreamAdapter(ImageInputStream pInput, long pLength, boolean pHasLength) {
         Validate.notNull(pInput, "stream");
-        Validate.isTrue(!pHasLength || pLength >= 0, pLength, "length < 0: %f");
+        Validate.isTrue(!pHasLength || pLength >= 0, pLength, "length < 0: %d");
 
         input = pInput;
         left = pLength;