diff --git a/include/spdk/string.h b/include/spdk/string.h
index e86653826..dbb78fd76 100644
--- a/include/spdk/string.h
+++ b/include/spdk/string.h
@@ -95,10 +95,8 @@ char *spdk_str_trim(char *s);
  * \param errnum Error code
  * \param buf Pointer to a buffer in which to place the error message
  * \param buflen the size of the buffer in bytes
- *
- * \return 0 upon success, a positive error number or -1 upon failure.
  */
-int spdk_strerror_r(int errnum, char *buf, size_t buflen);
+void spdk_strerror_r(int errnum, char *buf, size_t buflen);
 
 /**
  * Remove trailing newlines from the end of a string in place.
diff --git a/lib/util/string.c b/lib/util/string.c
index 44a178058..54f2abf9c 100644
--- a/lib/util/string.c
+++ b/lib/util/string.c
@@ -327,20 +327,27 @@ spdk_str_chomp(char *s)
 	return removed;
 }
 
-int
+void
 spdk_strerror_r(int errnum, char *buf, size_t buflen)
 {
+	int rc;
+
 #if defined(__USE_GNU)
 	char *new_buffer;
 	new_buffer = strerror_r(errnum, buf, buflen);
 	if (new_buffer != NULL) {
 		snprintf(buf, buflen, "%s", new_buffer);
-		return 0;
+		rc = 0;
+	} else {
+		rc = 1;
 	}
-	return 0;
 #else
-	return strerror_r(errnum, buf, buflen);
+	rc = strerror_r(errnum, buf, buflen);
 #endif
+
+	if (rc != 0) {
+		snprintf(buf, buflen, "Unknown error %d", errnum);
+	}
 }
 
 int