diff --git a/cores/stm32l4/Client.h b/cores/stm32l4/Client.h
index b8e5d935..eecffc07 100644
--- a/cores/stm32l4/Client.h
+++ b/cores/stm32l4/Client.h
@@ -32,7 +32,7 @@ class Client : public Stream {
   virtual size_t write(const uint8_t *buf, size_t size) =0;
   virtual int available() = 0;
   virtual int read() = 0;
-  virtual int read(uint8_t *buf, size_t size) = 0;
+  virtual size_t read(uint8_t *buf, size_t size) = 0;
   virtual int peek() = 0;
   virtual void flush() = 0;
   virtual void stop() = 0;