diff --git a/libguile/posix.c b/libguile/posix.c
index b0fcad5fd..088e75631 100644
--- a/libguile/posix.c
+++ b/libguile/posix.c
@@ -1209,6 +1209,13 @@ SCM_DEFINE (scm_execle, "execle", 2, 0, 1,
 #undef FUNC_NAME
 
 #ifdef HAVE_FORK
+static void *
+do_fork (void *pidp)
+{
+  * (int *) pidp = fork ();
+  return NULL;
+}
+
 SCM_DEFINE (scm_fork, "primitive-fork", 0, 0, 0,
             (),
 	    "Creates a new \"child\" process by duplicating the current \"parent\" process.\n"
@@ -1236,7 +1243,13 @@ SCM_DEFINE (scm_fork, "primitive-fork", 0, 0, 0,
         "         further behavior unspecified.  See \"Processes\" in the\n"
         "         manual, for more information.\n"),
        scm_current_warning_port ());
-  pid = fork ();
+
+  /* Take the alloc lock to make sure it is released when the child
+     process starts.  Failing to do that the child process could start
+     in a state where the alloc lock is taken and will never be
+     released.  */
+  GC_call_with_alloc_lock (do_fork, &pid);
+
   if (pid == -1)
     SCM_SYSERROR;
   return scm_from_int (pid);