diff --git a/src/hyperloglog.cpp b/src/hyperloglog.cpp
index 344fd219f..0b1239965 100644
--- a/src/hyperloglog.cpp
+++ b/src/hyperloglog.cpp
@@ -710,6 +710,7 @@ int hllSparseSet(robj *o, long index, uint8_t count) {
         first += span;
     }
     if (span == 0) return -1; /* Invalid format. */
+    if (p >= end) return -1; /* Invalid format. */
 
     next = HLL_SPARSE_IS_XZERO(p) ? p+2 : p+1;
     if (next >= end) next = NULL;