diff --git a/libc/unistd/sigblock.c b/libc/unistd/sigblock.c
index 863d7dad3..176bc1306 100644
--- a/libc/unistd/sigblock.c
+++ b/libc/unistd/sigblock.c
@@ -37,6 +37,7 @@ sigblock(int mask)
         sigset_t  the_sigset;
     } in, out;
 
+    sigemptyset(&in.the_sigset);
     in.the_mask = mask;
 
     n = sigprocmask(SIG_BLOCK, &in.the_sigset, &out.the_sigset);
diff --git a/libc/unistd/sigsetmask.c b/libc/unistd/sigsetmask.c
index 4f4645865..7842bf14b 100644
--- a/libc/unistd/sigsetmask.c
+++ b/libc/unistd/sigsetmask.c
@@ -38,6 +38,7 @@ sigsetmask(int mask)
         sigset_t  the_sigset;
     } in, out;
 
+    sigemptyset(&in.the_sigset);
     in.the_mask = mask;
 
     n = sigprocmask(SIG_SETMASK, &in.the_sigset, &out.the_sigset);