diff --git a/examples/apps/cli/main.c b/examples/apps/cli/main.c
index 4d20d4d6d..2a43f86b4 100644
--- a/examples/apps/cli/main.c
+++ b/examples/apps/cli/main.c
@@ -62,7 +62,7 @@ int main(int argc, char *argv[])
     otInstance *sInstance;
 
 #ifdef OPENTHREAD_MULTIPLE_INSTANCE
-    uint64_t otInstanceBufferLength = 0;
+    size_t otInstanceBufferLength = 0;
     uint8_t *otInstanceBuffer = NULL;
 #endif
 
diff --git a/examples/apps/ncp/main.c b/examples/apps/ncp/main.c
index 45f04d35b..20c0872bc 100644
--- a/examples/apps/ncp/main.c
+++ b/examples/apps/ncp/main.c
@@ -62,7 +62,7 @@ int main(int argc, char *argv[])
     otInstance *sInstance;
 
 #ifdef OPENTHREAD_MULTIPLE_INSTANCE
-    uint64_t otInstanceBufferLength = 0;
+    size_t otInstanceBufferLength = 0;
     uint8_t *otInstanceBuffer = NULL;
 #endif