diff --git a/radio/src/targets/simu/simpgmspace.cpp b/radio/src/targets/simu/simpgmspace.cpp
index e22a9e3ee..4b2f60aae 100644
--- a/radio/src/targets/simu/simpgmspace.cpp
+++ b/radio/src/targets/simu/simpgmspace.cpp
@@ -767,7 +767,7 @@ void auxSerialInit(unsigned int mode, unsigned int protocol)
 {
 }
 
-void auxSerialPutc(char c)
+void auxSerialPutc(uint8_t c)
 {
 }
 
@@ -792,7 +792,7 @@ void aux2SerialInit(unsigned int mode, unsigned int protocol)
 {
 }
 
-void aux2SerialPutc(char c)
+void aux2SerialPutc(uint8_t c)
 {
 }