diff --git a/tests/fuzz/fuzzer_platform.c b/tests/fuzz/fuzzer_platform.c
index 480e0f595..7357f40e3 100644
--- a/tests/fuzz/fuzzer_platform.c
+++ b/tests/fuzz/fuzzer_platform.c
@@ -420,6 +420,11 @@ otError otPlatUartSend(const uint8_t *aBuf, uint16_t aBufLength)
     return OT_ERROR_NONE;
 }
 
+otError otPlatUartFlush(void)
+{
+    return OT_ERROR_NOT_IMPLEMENTED;
+}
+
 void otPlatDiagProcess(otInstance *aInstance, int argc, char *argv[], char *aOutput, size_t aOutputMaxLen)
 {
     OT_UNUSED_VARIABLE(aInstance);