diff --git a/srcpkgs/runit/patches/chpst.patch b/srcpkgs/runit/patches/chpst.patch
new file mode 100644
index 00000000000..988c731c4be
--- /dev/null
+++ b/srcpkgs/runit/patches/chpst.patch
@@ -0,0 +1,14 @@
+Fix UB which breaks -n with negative values.
+Ensure optarg is incremented strictly before it is read from.
+
+--- runit-2.1.2/src/chpst.c.orig
++++ runit-2.1.2/src/chpst.c
+@@ -308,7 +308,7 @@
+     case 'n':
+       switch (*optarg) {
+         case '-':
+-          if (optarg[scan_ulong(++optarg, &ul)]) usage(); nicelvl =ul;
++          ++optarg; if (optarg[scan_ulong(optarg, &ul)]) usage(); nicelvl =ul;
+           nicelvl *=-1;
+           break;
+         case '+': ++optarg;
diff --git a/srcpkgs/runit/template b/srcpkgs/runit/template
index ca74abaf177..f139517ab48 100644
--- a/srcpkgs/runit/template
+++ b/srcpkgs/runit/template
@@ -1,7 +1,7 @@
 # Template file for 'runit'
 pkgname=runit
 version=2.1.2
-revision=12
+revision=13
 build_wrksrc="${pkgname}-${version}/src"
 build_style="gnu-makefile"
 short_desc="UNIX init scheme with service supervision"