diff --git a/src/proc.cpp b/src/proc.cpp
index a6da0c122..f31b720c4 100644
--- a/src/proc.cpp
+++ b/src/proc.cpp
@@ -354,10 +354,11 @@ typedef unsigned int process_generation_count_t;
 static std::vector<pid_t> s_disowned_pids;
 
 void add_disowned_pgid(pid_t pgid) {
-    // NEVER add our own pgid, or one of the special values,
-    // or waiting for it will
-    // snag other processes away.
-    if (pgid != getpgrp() && (pgid > 0 || pgid < -1)) {
+    // NEVER add our own (or an invalid) pgid as they are not unique to only
+    // one job, and may result in a deadlock if we attempt the wait.
+    if (pgid != getpgrp() && pgid > 0) {
+        // waitpid(2) is signalled to wait on a process group rather than a
+        // process id by using the negative of its value.
         s_disowned_pids.push_back(pgid * -1);
     }
 }