diff --git a/Gemfile.lock b/Gemfile.lock
index 143f06c997..60c127fca9 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -75,7 +75,7 @@ PATH
       activerecord (= 7.0.0.alpha)
       activesupport (= 7.0.0.alpha)
       marcel (~> 0.3.1)
-      mimemagic (~> 0.3.2)
+      mini_mime (~> 1.0.2)
     activesupport (7.0.0.alpha)
       concurrent-ruby (~> 1.0, >= 1.0.2)
       i18n (>= 1.6, < 2)
diff --git a/activestorage/activestorage.gemspec b/activestorage/activestorage.gemspec
index e3a4c13149..28a55b9ba6 100644
--- a/activestorage/activestorage.gemspec
+++ b/activestorage/activestorage.gemspec
@@ -37,5 +37,5 @@ Gem::Specification.new do |s|
   s.add_dependency "activerecord",  version
 
   s.add_dependency "marcel",    "~> 0.3.1"
-  s.add_dependency "mimemagic", "~> 0.3.2"
+  s.add_dependency "mini_mime", "~> 1.0.2"
 end
diff --git a/activestorage/app/models/active_storage/blob/representable.rb b/activestorage/app/models/active_storage/blob/representable.rb
index 065ac3ad0c..e2c2663331 100644
--- a/activestorage/app/models/active_storage/blob/representable.rb
+++ b/activestorage/app/models/active_storage/blob/representable.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require "mimemagic"
+require "mini_mime"
 
 module ActiveStorage::Blob::Representable
   extend ActiveSupport::Concern
@@ -110,10 +110,10 @@ module ActiveStorage::Blob::Representable
     end
 
     def format
-      if filename.extension.present? && MimeMagic.by_extension(filename.extension)&.to_s == content_type
+      if filename.extension.present? && MiniMime.lookup_by_extension(filename.extension)&.content_type == content_type
         filename.extension
       else
-        MimeMagic.new(content_type).extensions.first
+        MiniMime.lookup_by_content_type(content_type).extension
       end
     end
 
diff --git a/activestorage/app/models/active_storage/variation.rb b/activestorage/app/models/active_storage/variation.rb
index 8aa36f005e..70979b613e 100644
--- a/activestorage/app/models/active_storage/variation.rb
+++ b/activestorage/app/models/active_storage/variation.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require "mimemagic"
+require "mini_mime"
 
 # A set of transformations that can be applied to a blob to create a variant. This class is exposed via
 # the ActiveStorage::Blob#variant method and should rarely be used directly.
@@ -59,14 +59,14 @@ class ActiveStorage::Variation
 
   def format
     transformations.fetch(:format, :png).tap do |format|
-      if MimeMagic.by_extension(format).nil?
+      if MiniMime.lookup_by_extension(format.to_s).nil?
         raise ArgumentError, "Invalid variant format (#{format.inspect})"
       end
     end
   end
 
   def content_type
-    MimeMagic.by_extension(format).to_s
+    MiniMime.lookup_by_extension(format.to_s).content_type
   end
 
   # Returns a signed key for all the +transformations+ that this variation was instantiated with.