diff --git a/defs.h b/defs.h
index 4e06a92..22e847b 100644
--- a/defs.h
+++ b/defs.h
@@ -712,13 +712,13 @@
 extern int loop_ioctl(struct tcb *, long, long);
 extern int ptp_ioctl(struct tcb *, long, long);
 
-extern int tv_nz(struct timeval *);
-extern int tv_cmp(struct timeval *, struct timeval *);
-extern double tv_float(struct timeval *);
-extern void tv_add(struct timeval *, struct timeval *, struct timeval *);
-extern void tv_sub(struct timeval *, struct timeval *, struct timeval *);
-extern void tv_mul(struct timeval *, struct timeval *, int);
-extern void tv_div(struct timeval *, struct timeval *, int);
+extern int tv_nz(const struct timeval *);
+extern int tv_cmp(const struct timeval *, const struct timeval *);
+extern double tv_float(const struct timeval *);
+extern void tv_add(struct timeval *, const struct timeval *, const struct timeval *);
+extern void tv_sub(struct timeval *, const struct timeval *, const struct timeval *);
+extern void tv_mul(struct timeval *, const struct timeval *, int);
+extern void tv_div(struct timeval *, const struct timeval *, int);
 
 /* Strace log generation machinery.
  *