diff --git a/src/layer/argmax.cpp b/src/layer/argmax.cpp
index d6933387e..3ede2a0db 100644
--- a/src/layer/argmax.cpp
+++ b/src/layer/argmax.cpp
@@ -22,6 +22,7 @@ DEFINE_LAYER_CREATOR(ArgMax)
 
 ArgMax::ArgMax()
 {
+    one_blob_only = true;
 }
 
 int ArgMax::load_param(const ParamDict& pd)