diff --git a/sdk/plugins/regions.cpp b/sdk/plugins/regions.cpp
index ec8f66a..561fc74 100644
--- a/sdk/plugins/regions.cpp
+++ b/sdk/plugins/regions.cpp
@@ -86,6 +86,8 @@ class Cat : public UntrainableMetaTransform
     {
         dst.file = src.file;
 
+        if (src.size() % partitions != 0)
+            qFatal("Cat %d partitions does not evenly divide %d matrices.", partitions, src.size());
         QVector<int> sizes(partitions, 0);
         for (int i=0; i<src.size(); i++)
             sizes[i%partitions] += src[i].total() * src[i].channels();