diff --git a/core/src/main/java/org/apache/spark/unsafe/map/BytesToBytesMap.java b/core/src/main/java/org/apache/spark/unsafe/map/BytesToBytesMap.java
index b15365fe54ad6..7590b72112c54 100644
--- a/core/src/main/java/org/apache/spark/unsafe/map/BytesToBytesMap.java
+++ b/core/src/main/java/org/apache/spark/unsafe/map/BytesToBytesMap.java
@@ -741,7 +741,9 @@ public boolean append(Object kbase, long koff, int klen, Object vbase, long voff
         longArray.set(pos * 2 + 1, keyHashcode);
         isDefined = true;
 
-        if (numKeys >= growthThreshold && longArray.size() < MAX_CAPACITY) {
+        // We use two array entries per key, so the array size is twice the capacity.
+        // We should compare the current capacity of the array, instead of its size.
+        if (numKeys >= growthThreshold && longArray.size() / 2 < MAX_CAPACITY) {
           try {
             growAndRehash();
           } catch (SparkOutOfMemoryError oom) {