diff --git a/imageio/imageio-tiff/src/main/java/com/twelvemonkeys/imageio/plugins/tiff/TIFFImageReader.java b/imageio/imageio-tiff/src/main/java/com/twelvemonkeys/imageio/plugins/tiff/TIFFImageReader.java
index 2fccfe72..01398695 100644
--- a/imageio/imageio-tiff/src/main/java/com/twelvemonkeys/imageio/plugins/tiff/TIFFImageReader.java
+++ b/imageio/imageio-tiff/src/main/java/com/twelvemonkeys/imageio/plugins/tiff/TIFFImageReader.java
@@ -525,6 +525,9 @@ public class TIFFImageReader extends ImageReaderBase {
                     }
 
                     yCbCrPos = getValueAsIntWithDefault(TIFF.TAG_YCBCR_POSITIONING, TIFFExtension.YCBCR_POSITIONING_CENTERED);
+                    if (yCbCrPos != TIFFExtension.YCBCR_POSITIONING_CENTERED && yCbCrPos != TIFFExtension.YCBCR_POSITIONING_COSITED) {
+                        processWarningOccurred("Uknown TIFF YCbCrPositioning value, expected 1 or 2: " + yCbCrPos);
+                    }
 
                     Entry subSampling = currentIFD.getEntryById(TIFF.TAG_YCBCR_SUB_SAMPLING);