diff --git a/mach/proto/as/comm7.c b/mach/proto/as/comm7.c
index 7c976cdf..492a2444 100644
--- a/mach/proto/as/comm7.c
+++ b/mach/proto/as/comm7.c
@@ -12,7 +12,11 @@
 #include	"comm1.h"
 #include	"y.tab.h"
 
-extern char	*sprintf();
+#ifndef __STDC__
+extern char *sprintf();
+#else
+/* sprintf should be declared in stdio.h, as returning an int */
+#endif
 
 valu_t
 load(ip)
diff --git a/mach/proto/ncg/compute.c b/mach/proto/ncg/compute.c
index eb75f93e..1d66c749 100644
--- a/mach/proto/ncg/compute.c
+++ b/mach/proto/ncg/compute.c
@@ -19,7 +19,11 @@ static char rcsid[] = "$Header$";
  * Author: Hans van Staveren
  */
 
-extern char	*sprintf();
+#ifndef __STDC__
+extern char *sprintf();
+#else
+/* sprintf should be declared in stdio.h, as returning an int */
+#endif
 
 #define LLEAF 01
 #define LDEF  02
diff --git a/mach/proto/ncg/fillem.c b/mach/proto/ncg/fillem.c
index dd95f980..99350002 100644
--- a/mach/proto/ncg/fillem.c
+++ b/mach/proto/ncg/fillem.c
@@ -29,7 +29,11 @@ static char rcsid2[] = "$Header$";
  * Author: Hans van Staveren
  */
 
-extern char	*sprintf();
+#ifndef __STDC__
+extern char *sprintf();
+#else
+/* sprintf should be declared in stdio.h, as returning an int */
+#endif
 
 #ifndef newplb			/* retrofit for older mach.h */
 #define newplb newilb
diff --git a/mach/proto/ncg/gencode.c b/mach/proto/ncg/gencode.c
index 7d62a381..12cf181b 100644
--- a/mach/proto/ncg/gencode.c
+++ b/mach/proto/ncg/gencode.c
@@ -19,7 +19,11 @@ static char rcsid[] = "$Header$";
  * Author: Hans van Staveren
  */
 
-extern char	*sprintf();
+#ifndef __STDC__
+extern char *sprintf();
+#else
+/* sprintf should be declared in stdio.h, as returning an int */
+#endif
 
 string mystrcpy();
 
diff --git a/util/cgg/main.c b/util/cgg/main.c
index f8e2747a..7bf82b1e 100644
--- a/util/cgg/main.c
+++ b/util/cgg/main.c
@@ -7,7 +7,12 @@
 
 #include "booth.h"
 
-char *strncpy(), *strcpy(), *sprintf();
+extern char *strncpy(), *strcpy();
+#ifndef __STDC__
+extern char *sprintf();
+#else
+/* sprintf should be declared in stdio.h, as returning an int */
+#endif
 
 char * myalloc(n) {
 	register char *p;