diff --git a/admin/solidus_admin.gemspec b/admin/solidus_admin.gemspec
index d9290e887d..c72c5815dc 100644
--- a/admin/solidus_admin.gemspec
+++ b/admin/solidus_admin.gemspec
@@ -30,6 +30,8 @@ Gem::Specification.new do |s|
 
   s.add_dependency "blueprinter"
   s.add_dependency "geared_pagination", "~> 1.1"
+  # Rails < 8.1 isn't compatible with json 3.x
+  s.add_dependency "json", "< 3"
   s.add_dependency "importmap-rails", [">= 2.0", "< 3"]
   s.add_dependency "solidus_backend"
   s.add_dependency "solidus_core", "> 4.2"
diff --git a/core/solidus_core.gemspec b/core/solidus_core.gemspec
index a5c5d947fc..705b6479ed 100644
--- a/core/solidus_core.gemspec
+++ b/core/solidus_core.gemspec
@@ -42,6 +42,7 @@ Gem::Specification.new do |s|
   s.add_dependency "discard", "~> 2.0"
   s.add_dependency "friendly_id", "~> 5.0"
   s.add_dependency "image_processing", "~> 1.10"
+  s.add_dependency "json", "< 3"
   s.add_dependency "mini_magick", "~> 4.10"
   s.add_dependency "monetize", "~> 1.8"
   s.add_dependency "kt-paperclip", [">= 6.3", "< 8.1"]