diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index dad5f624bd..bc07a84f4d 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -12,6 +12,10 @@
 #include <fcntl.h>
 #include <limits.h>
 
+#ifdef __APPLE__
+#include <sys/syscall.h>
+#endif
+
 #include "util.hh"
 
 
@@ -851,7 +855,16 @@ void killUser(uid_t uid)
                 throw SysError("setting uid");
 
             while (true) {
+#ifdef __APPLE__
+                /* OSX's kill syscall takes a third parameter that, among other
+                   things, determines if kill(-1, signo) affects the calling
+                   process. In the OSX libc, it's set to true, which means
+                   "follow POSIX", which we don't want here
+                 */
+                if (syscall(SYS_kill, -1, SIGKILL, false) == 0) break;
+#else
                 if (kill(-1, SIGKILL) == 0) break;
+#endif
                 if (errno == ESRCH) break; /* no more processes */
                 if (errno != EINTR)
                     throw SysError(format("cannot kill processes for uid `%1%'") % uid);