diff --git a/spec/std/http/spec_helper.cr b/spec/std/http/spec_helper.cr
index 4b04204cd383..d7829553aeda 100644
--- a/spec/std/http/spec_helper.cr
+++ b/spec/std/http/spec_helper.cr
@@ -4,6 +4,9 @@ require "../../support/fibers"
 
 private def wait_for
   timeout = {% if flag?(:interpreted) %}
+              # TODO: it's not clear why some interpreter specs
+              # take more than 5 seconds to bind to a server.
+              # See #12429.
               25.seconds
             {% else %}
               5.seconds
diff --git a/spec/support/channel.cr b/spec/support/channel.cr
index 96d9a9c3b723..9fbf40e60b4f 100644
--- a/spec/support/channel.cr
+++ b/spec/support/channel.cr
@@ -1,6 +1,13 @@
 def schedule_timeout(c : Channel(Symbol))
   spawn do
-    sleep 1
+    {% if flag?(:interpreted) %}
+      # TODO: it's not clear why some interpreter specs
+      # take more than 1 second in some cases.
+      # See #12429.
+      sleep 5
+    {% else %}
+      sleep 1
+    {% end %}
     c.send(:timeout)
   end
 end