diff --git a/src/gdb.h b/src/gdb.h
index 3678e76..693a4b5 100644
--- a/src/gdb.h
+++ b/src/gdb.h
@@ -29,8 +29,8 @@
 }
 
 /* These functions must be defined by the application */
-unsigned char gdb_getDebugChar(void);
-void gdb_putDebugChar(unsigned char ch);
+unsigned char gdb_getDebugChar(void) FASTCALL;
+void gdb_putDebugChar(unsigned char ch) FASTCALL;
 
 /* This file contains the library exports. */
 
diff --git a/src/lib.c b/src/lib.c
index 56cee13..1cff7a5 100644
--- a/src/lib.c
+++ b/src/lib.c
@@ -69,10 +69,6 @@ byte _gdb_state[NUMREGBYTES];
 #error "Too small DBG_PACKET_SIZE"
 #endif
 
-#ifndef FASTCALL
-#define FASTCALL __z88dk_fastcall
-#endif
-
 #ifndef DBG_ENTER
 #define DBG_ENTER
 #else
diff --git a/src/lib.h b/src/lib.h
index d5734b9..e575dc6 100644
--- a/src/lib.h
+++ b/src/lib.h
@@ -21,6 +21,10 @@
 #ifndef __GDB_LIB_H__
 #define __GDB_LIB_H__
 
+#ifndef FASTCALL
+#define FASTCALL __z88dk_fastcall
+#endif
+
 typedef unsigned char byte;
 typedef unsigned short word;