diff --git a/src/fish.cpp b/src/fish.cpp
index 572fbe3e0..eaef8755e 100644
--- a/src/fish.cpp
+++ b/src/fish.cpp
@@ -324,7 +324,7 @@ int main(int argc, char **argv) {
     program_name = L"fish";
     set_main_thread();
     setup_fork_guards();
-
+    signal_unblock_all();
     setlocale(LC_ALL, "");
     fish_setlocale();
 
diff --git a/src/signal.cpp b/src/signal.cpp
index 93709a287..c3766d9de 100644
--- a/src/signal.cpp
+++ b/src/signal.cpp
@@ -387,6 +387,13 @@ void signal_block(bool force) {
     // debug( 0, L"signal block level increased to %d", block_count );
 }
 
+/// Ensure we did not inherit any blocked signals. See issue #3964.
+void signal_unblock_all() {
+    sigset_t iset;
+    sigemptyset(&iset);
+    sigprocmask(SIG_SETMASK, &iset, NULL);
+}
+
 void signal_unblock(bool force) {
     if (!force && ignore_signal_block) return;
 
diff --git a/src/signal.h b/src/signal.h
index 436945105..06fe37cf9 100644
--- a/src/signal.h
+++ b/src/signal.h
@@ -26,6 +26,9 @@ void signal_set_handlers();
 /// default action (SIG_DFL) will be set
 void signal_handle(int sig, int do_handle);
 
+/// Ensure we did not inherit any blocked signals. See issue #3964.
+void signal_unblock_all();
+
 /// Block all signals.
 void signal_block(bool force = false);