diff --git a/code/common/model/src/main/java/nu/marginalia/model/idx/WordMetadata.java b/code/common/model/src/main/java/nu/marginalia/model/idx/WordMetadata.java
index 81f1aa33..95c2c407 100644
--- a/code/common/model/src/main/java/nu/marginalia/model/idx/WordMetadata.java
+++ b/code/common/model/src/main/java/nu/marginalia/model/idx/WordMetadata.java
@@ -13,6 +13,12 @@ public record WordMetadata(int tfIdf,
                            int positions,
                            int count,
                            byte flags) {
+    public WordMetadata {
+        if (WordMetadata.class.desiredAssertionStatus()) {
+            // invariant checks go here
+            assert(Integer.bitCount(positions) <= count);
+        }
+    }
 
     public static final long COUNT_MASK = 0xFL;
     public static final int COUNT_SHIFT = 8;