diff --git a/src/crystal/system/unix/process.cr b/src/crystal/system/unix/process.cr
index 420030f8ba53..0eb58231900e 100644
--- a/src/crystal/system/unix/process.cr
+++ b/src/crystal/system/unix/process.cr
@@ -176,7 +176,14 @@ struct Crystal::System::Process
     newmask = uninitialized LibC::SigsetT
     oldmask = uninitialized LibC::SigsetT
 
+    # block signals while we fork, so the child process won't forward signals it
+    # may receive to the parent through the signal pipe, but make sure to not
+    # block stop-the-world signals as it appears to create deadlocks in glibc
+    # for example; this is safe because these signal handlers musn't be
+    # registered through `Signal.trap` but directly through `sigaction`.
     LibC.sigfillset(pointerof(newmask))
+    LibC.sigdelset(pointerof(newmask), System::Thread.sig_suspend)
+    LibC.sigdelset(pointerof(newmask), System::Thread.sig_resume)
     ret = LibC.pthread_sigmask(LibC::SIG_SETMASK, pointerof(newmask), pointerof(oldmask))
     raise RuntimeError.from_errno("Failed to disable signals") unless ret == 0
 
diff --git a/src/crystal/system/unix/pthread.cr b/src/crystal/system/unix/pthread.cr
index 50a0fc56e818..bbdfcbc3d41c 100644
--- a/src/crystal/system/unix/pthread.cr
+++ b/src/crystal/system/unix/pthread.cr
@@ -249,7 +249,8 @@ module Crystal::System::Thread
     end
   end
 
-  # the suspend/resume signals follow BDWGC
+  # the suspend/resume signals try to follow BDWGC but aren't exact (e.g. it may
+  # use SIGUSR1 and SIGUSR2 on FreeBSD instead of SIGRT).
 
   private SIG_SUSPEND =
     {% if flag?(:linux) %}
@@ -266,6 +267,22 @@ module Crystal::System::Thread
     {% else %}
       LibC::SIGXCPU
     {% end %}
+
+  def self.sig_suspend : ::Signal
+    if GC.responds_to?(:sig_suspend)
+      GC.sig_suspend
+    else
+      ::Signal.new(SIG_SUSPEND)
+    end
+  end
+
+  def self.sig_resume : ::Signal
+    if GC.responds_to?(:sig_resume)
+      GC.sig_resume
+    else
+      ::Signal.new(SIG_RESUME)
+    end
+  end
 end
 
 # In musl (alpine) the calls to unwind API segfaults
diff --git a/src/gc/boehm.cr b/src/gc/boehm.cr
index 41c0f43f2a8c..33d6466d792b 100644
--- a/src/gc/boehm.cr
+++ b/src/gc/boehm.cr
@@ -164,6 +164,8 @@ lib LibGC
 
   fun stop_world_external = GC_stop_world_external
   fun start_world_external = GC_start_world_external
+  fun get_suspend_signal = GC_get_suspend_signal : Int
+  fun get_thr_restart_signal = GC_get_thr_restart_signal : Int
 end
 
 module GC
@@ -483,4 +485,16 @@ module GC
   def self.start_world : Nil
     LibGC.start_world_external
   end
+
+  {% if flag?(:unix) %}
+    # :nodoc:
+    def self.sig_suspend : Signal
+      Signal.new(LibGC.get_suspend_signal)
+    end
+
+    # :nodoc:
+    def self.sig_resume : Signal
+      Signal.new(LibGC.get_thr_restart_signal)
+    end
+  {% end %}
 end