diff --git a/include/spdk/cpuset.h b/include/spdk/cpuset.h
index 59f98d421..1e0f73aae 100644
--- a/include/spdk/cpuset.h
+++ b/include/spdk/cpuset.h
@@ -136,8 +136,10 @@ uint32_t spdk_cpuset_count(const struct spdk_cpuset *set);
  * \param CPU set.
  * \return Pointer to hexadecimal representation of CPU set. Buffer to store a
  * string is dynamically allocated internally and freed with CPU set object.
+ * Memory returned by this function might be changed after subsequent calls to
+ * this function so string should be copied by user.
  */
-char *spdk_cpuset_fmt(struct spdk_cpuset *set);
+const char *spdk_cpuset_fmt(struct spdk_cpuset *set);
 
 /**
  * Convert a string containing a CPU core mask into a CPU set.
diff --git a/lib/util/cpuset.c b/lib/util/cpuset.c
index 6d74ea77e..1a02e59fe 100644
--- a/lib/util/cpuset.c
+++ b/lib/util/cpuset.c
@@ -132,7 +132,7 @@ spdk_cpuset_count(const struct spdk_cpuset *set)
 	return count;
 }
 
-char *
+const char *
 spdk_cpuset_fmt(struct spdk_cpuset *set)
 {
 	uint32_t lcore, lcore_max = 0;
diff --git a/test/unit/lib/util/cpuset.c/cpuset_ut.c b/test/unit/lib/util/cpuset.c/cpuset_ut.c
index 058b6c049..6fea0ad3e 100644
--- a/test/unit/lib/util/cpuset.c/cpuset_ut.c
+++ b/test/unit/lib/util/cpuset.c/cpuset_ut.c
@@ -189,7 +189,7 @@ test_cpuset_fmt(void)
 	int i;
 	uint32_t lcore;
 	struct spdk_cpuset *core_mask = spdk_cpuset_alloc();
-	char *hex_mask;
+	const char *hex_mask;
 	char hex_mask_ref[SPDK_CPUSET_SIZE / 4 + 1];
 
 	/* Clear coremask. hex_mask should be "0" */