diff --git a/mingw-w64-crt/profile/gmon.c b/mingw-w64-crt/profile/gmon.c
index adaf2bc..41fe48a 100644
--- a/mingw-w64-crt/profile/gmon.c
+++ b/mingw-w64-crt/profile/gmon.c
@@ -76,10 +76,10 @@
     return malloc(size);
 }
 
+void monstartup (size_t, size_t);
+
 void
-monstartup(lowpc, highpc)
-	size_t lowpc;
-	size_t highpc;
+monstartup (size_t lowpc, size_t highpc)
 {
 	register size_t o;
 	char *cp;
@@ -143,8 +143,9 @@
 	moncontrol(1);
 }
 
+void _mcleanup (void);
 void
-_mcleanup()
+_mcleanup(void)
 {
 	int fd;
 	int hz;
@@ -270,8 +271,7 @@
  *	all the data structures are ready.
  */
 void
-moncontrol(mode)
-	int mode;
+moncontrol(int mode)
 {
 	struct gmonparam *p = &_gmonparam;
 
diff --git a/mingw-w64-crt/profile/mcount.c b/mingw-w64-crt/profile/mcount.c
index d61da00..4df6c57 100644
--- a/mingw-w64-crt/profile/mcount.c
+++ b/mingw-w64-crt/profile/mcount.c
@@ -62,6 +62,8 @@
  * perform this optimization.
  */
 /* _mcount; may be static, inline, etc */
+_MCOUNT_DECL (size_t, size_t);
+
 _MCOUNT_DECL (size_t frompc, size_t selfpc)
 {
 	register u_short *frompcindex;