diff --git a/lib/libc/db/test/dbtest.c b/lib/libc/db/test/dbtest.c
index ebf6be883be4..be433c0a3040 100644
--- a/lib/libc/db/test/dbtest.c
+++ b/lib/libc/db/test/dbtest.c
@@ -64,7 +64,7 @@ enum S { COMMAND, COMPARE, GET, PUT, REMOVE, SEQ, SEQFLAG, KEY, DATA };
 void	 compare __P((DBT *, DBT *));
 DBTYPE	 dbtype __P((char *));
 void	 dump __P((DB *, int));
-void	 err __P((const char *, ...));
+void	 err __P((const char *, ...)) __printflike(1, 2);
 void	 get __P((DB *, DBT *));
 void	 getdata __P((DB *, DBT *, DBT *));
 void	 put __P((DB *, DBT *, DBT *));
diff --git a/lib/libc/net/gethostbydns.c b/lib/libc/net/gethostbydns.c
index 4a566557d3c0..a11364076012 100644
--- a/lib/libc/net/gethostbydns.c
+++ b/lib/libc/net/gethostbydns.c
@@ -98,6 +98,10 @@ static u_char host_addr[16];	/* IPv4 or IPv6 */
 static void addrsort __P((char **, int));
 #endif
 
+#ifdef DEBUG
+static void dprintf(char *, int) __printflike(1, 0);
+#endif
+
 #if PACKETSZ > 1024
 #define	MAXPACKET	PACKETSZ
 #else
diff --git a/lib/libc/stdio/vfprintf.c b/lib/libc/stdio/vfprintf.c
index 49d4971270d2..11f2b21d6b21 100644
--- a/lib/libc/stdio/vfprintf.c
+++ b/lib/libc/stdio/vfprintf.c
@@ -71,7 +71,7 @@ static const char rcsid[] =
 #define	FLOATING_POINT
 
 static int	__sprint __P((FILE *, struct __suio *));
-static int	__sbprintf __P((FILE *, const char *, va_list));
+static int	__sbprintf __P((FILE *, const char *, va_list)) __printflike(2, 0);
 static char *	__ultoa __P((u_long, char *, int, int, char *));
 static char *	__uqtoa __P((u_quad_t, char *, int, int, char *));
 static void	__find_arguments __P((const char *, va_list, void ***));
diff --git a/lib/libc_r/test/mutex_d.c b/lib/libc_r/test/mutex_d.c
index ea31299e1aef..21bf84850060 100644
--- a/lib/libc_r/test/mutex_d.c
+++ b/lib/libc_r/test/mutex_d.c
@@ -59,6 +59,9 @@
 
 #define MAX_THREAD_CMDS	10
 
+static void log_error(const char *, ...) __printflike(1, 2);
+static void log_trace (const char *, ...) __printflike(1, 2);
+static void log (const char *, ...) __printflike(1, 2);
 
 /*------------------------------------------------------------
  * Types
diff --git a/lib/libcam/camlib.h b/lib/libcam/camlib.h
index 420129431b0c..8d1823a7c0b9 100644
--- a/lib/libcam/camlib.h
+++ b/lib/libcam/camlib.h
@@ -150,11 +150,11 @@ int			cam_get_device(const char *path, char *dev_name,
 /*
  * Buffer encoding/decoding routines, from the old SCSI library.
  */
-int csio_decode(struct ccb_scsiio *csio, char *fmt, ...);
+int csio_decode(struct ccb_scsiio *csio, char *fmt, ...) __printflike(2, 3);
 int csio_decode_visit(struct ccb_scsiio *csio, char *fmt,
 		      void (*arg_put)(void *, int, void *, int, char *),
 		      void *puthook);
-int buff_decode(u_int8_t *buff, size_t len, char *fmt, ...);
+int buff_decode(u_int8_t *buff, size_t len, char *fmt, ...) __printflike(3, 4);
 int buff_decode_visit(u_int8_t *buff, size_t len, char *fmt,
 		      void (*arg_put)(void *, int, void *, int, char *),
 		      void *puthook);
@@ -166,7 +166,7 @@ int csio_build_visit(struct ccb_scsiio *csio, u_int8_t *data_ptr,
 		     int timeout, char *cmd_spec,
 		     int (*arg_get)(void *hook, char *field_name),
 		     void *gethook);
-int csio_encode(struct ccb_scsiio *csio, char *fmt, ...);
+int csio_encode(struct ccb_scsiio *csio, char *fmt, ...) __printflike(2, 3);
 int buff_encode_visit(u_int8_t *buff, size_t len, char *fmt,
 		      int (*arg_get)(void *hook, char *field_name),
 		      void *gethook);
diff --git a/lib/libdisk/create_chunk.c b/lib/libdisk/create_chunk.c
index 366e3738e767..567bea4806f5 100644
--- a/lib/libdisk/create_chunk.c
+++ b/lib/libdisk/create_chunk.c
@@ -27,6 +27,8 @@
 #include <pwd.h>
 #include "libdisk.h"
 
+static void msgDebug(char *, ...) __printflike(1, 2);
+
 /* Clone these two from sysinstall because we need our own copies
  * due to link order problems with `crunch'.  Feh!
  */
diff --git a/lib/libkse/test/mutex_d.c b/lib/libkse/test/mutex_d.c
index ea31299e1aef..21bf84850060 100644
--- a/lib/libkse/test/mutex_d.c
+++ b/lib/libkse/test/mutex_d.c
@@ -59,6 +59,9 @@
 
 #define MAX_THREAD_CMDS	10
 
+static void log_error(const char *, ...) __printflike(1, 2);
+static void log_trace (const char *, ...) __printflike(1, 2);
+static void log (const char *, ...) __printflike(1, 2);
 
 /*------------------------------------------------------------
  * Types
diff --git a/lib/libkvm/kvm_private.h b/lib/libkvm/kvm_private.h
index 402b9ee6d849..85d790f882d5 100644
--- a/lib/libkvm/kvm_private.h
+++ b/lib/libkvm/kvm_private.h
@@ -70,7 +70,7 @@ struct __kvm {
 /*
  * Functions used internally by kvm, but across kvm modules.
  */
-void	 _kvm_err __P((kvm_t *kd, const char *program, const char *fmt, ...));
+void	 _kvm_err __P((kvm_t *kd, const char *program, const char *fmt, ...)) __printflike(3, 4);
 void	 _kvm_freeprocs __P((kvm_t *kd));
 void	 _kvm_freevtop __P((kvm_t *));
 int	 _kvm_initvtop __P((kvm_t *));
@@ -78,5 +78,5 @@ int	 _kvm_kvatop __P((kvm_t *, u_long, u_long *));
 void	*_kvm_malloc __P((kvm_t *kd, size_t));
 void	*_kvm_realloc __P((kvm_t *kd, void *, size_t));
 void	 _kvm_syserr
-	    __P((kvm_t *kd, const char *program, const char *fmt, ...));
+	    __P((kvm_t *kd, const char *program, const char *fmt, ...)) __printflike(3, 4);
 int	 _kvm_uvatop __P((kvm_t *, const struct proc *, u_long, u_long *));
diff --git a/lib/libncp/ncpl_subr.c b/lib/libncp/ncpl_subr.c
index 0a36126079a6..768c183ff56a 100644
--- a/lib/libncp/ncpl_subr.c
+++ b/lib/libncp/ncpl_subr.c
@@ -435,7 +435,7 @@ ncp_args_parseopt(struct ncp_args *na, int opt, char *optarg, ncp_setopt_t *set_
  *  the rest - requester error;
  */
 void
-ncp_error(char *fmt, int error,...) {
+ncp_error(const char *fmt, int error, ...) {
 	va_list ap;
 
 	fprintf(stderr, "%s: ", __progname);
diff --git a/lib/libnetgraph/netgraph.h b/lib/libnetgraph/netgraph.h
index c5a87cb4bc93..d0f402ca6aa0 100644
--- a/lib/libnetgraph/netgraph.h
+++ b/lib/libnetgraph/netgraph.h
@@ -48,9 +48,9 @@
 
 __BEGIN_DECLS
 int	NgMkSockNode(const char *, int *, int *);
-int	NgNameNode(int, const char *, const char *, ...);
+int	NgNameNode(int, const char *, const char *, ...) __printflike(3, 4);
 int	NgSendMsg(int, const char *, int, int, const void *, size_t);
-int	NgSendAsciiMsg(int, const char *, const char *, ...);
+int	NgSendAsciiMsg(int, const char *, const char *, ...) __printflike(3, 4);
 int	NgSendReplyMsg(int, const char *,
 		const struct ng_mesg *, const void *, size_t);
 int	NgRecvMsg(int, struct ng_mesg *, size_t, char *);
diff --git a/lib/libpthread/test/mutex_d.c b/lib/libpthread/test/mutex_d.c
index ea31299e1aef..21bf84850060 100644
--- a/lib/libpthread/test/mutex_d.c
+++ b/lib/libpthread/test/mutex_d.c
@@ -59,6 +59,9 @@
 
 #define MAX_THREAD_CMDS	10
 
+static void log_error(const char *, ...) __printflike(1, 2);
+static void log_trace (const char *, ...) __printflike(1, 2);
+static void log (const char *, ...) __printflike(1, 2);
 
 /*------------------------------------------------------------
  * Types
diff --git a/sys/netncp/ncp_lib.h b/sys/netncp/ncp_lib.h
index d99d03f97816..e1fee6c46165 100644
--- a/sys/netncp/ncp_lib.h
+++ b/sys/netncp/ncp_lib.h
@@ -168,7 +168,7 @@ NWCCODE NWDisableTTS(NWCONN_HANDLE);
 NWCCODE NWEnableTTS(NWCONN_HANDLE);
 NWCCODE NWDisableFileServerLogin(NWCONN_HANDLE);
 NWCCODE NWEnableFileServerLogin(NWCONN_HANDLE);
-void ncp_error(char *, int,...);
+void ncp_error(const char *, int, ...) __printf0like(1, 3);
 char *ncp_printb(char *, int, const struct ncp_bitname *);
 void nw_keyhash(const u_char *, const u_char *, int, u_char *);
 void nw_encrypt(const u_char *, const u_char *, u_char *);