diff --git a/CHANGELOG.md b/CHANGELOG.md
index 536cd7db..5e9b8977 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@
 - Drop support for the HS512256 algorithm [#650](https://github.com/jwt/ruby-jwt/pull/650) ([@anakinj](https://github.com/anakinj))
 - Remove deprecated claim verification methods [#654](https://github.com/jwt/ruby-jwt/pull/654) ([@anakinj](https://github.com/anakinj))
 - Remove dependency to rbnacl [#655](https://github.com/jwt/ruby-jwt/pull/655) ([@anakinj](https://github.com/anakinj))
+- Support only stricter base64 decoding (RFC 4648) [#658](https://github.com/jwt/ruby-jwt/pull/658) ([@anakinj](https://github.com/anakinj))
 
 Take a look at the [upgrade guide](UPGRADING.md) for more details.
 
diff --git a/lib/jwt/base64.rb b/lib/jwt/base64.rb
index 14c9db28..fdf1bf95 100644
--- a/lib/jwt/base64.rb
+++ b/lib/jwt/base64.rb
@@ -14,22 +14,13 @@ def url_encode(str)
       end
 
       # Decode a string with URL-safe Base64 complying with RFC 4648.
-      # Deprecated support for RFC 2045 remains for now. ("All line breaks or other characters not found in Table 1 must be ignored by decoding software")
       # @api private
       def url_decode(str)
         ::Base64.urlsafe_decode64(str)
       rescue ArgumentError => e
         raise unless e.message == 'invalid base64'
-        raise Base64DecodeError, 'Invalid base64 encoding' if JWT.configuration.strict_base64_decoding
 
-        loose_urlsafe_decode64(str).tap do
-          Deprecations.warning('Invalid base64 input detected, could be because of invalid padding, trailing whitespaces or newline chars. Graceful handling of invalid input will be dropped in the next major version of ruby-jwt', only_if_valid: true)
-        end
-      end
-
-      def loose_urlsafe_decode64(str)
-        str += '=' * (4 - str.length.modulo(4))
-        ::Base64.decode64(str.tr('-_', '+/'))
+        raise Base64DecodeError, 'Invalid base64 encoding'
       end
     end
   end
diff --git a/spec/jwt/jwt_spec.rb b/spec/jwt/jwt_spec.rb
index 7488e438..dd919498 100644
--- a/spec/jwt/jwt_spec.rb
+++ b/spec/jwt/jwt_spec.rb
@@ -552,14 +552,14 @@
   end
 
   context 'a token with invalid Base64 segments' do
-    it 'raises JWT::DecodeError' do
-      expect { JWT.decode('hello.there.world') }.to raise_error(JWT::DecodeError, 'Invalid segment encoding')
+    it 'raises JWT::Base64DecodeError' do
+      expect { JWT.decode('hello.there.world') }.to raise_error(JWT::Base64DecodeError, 'Invalid base64 encoding')
     end
   end
 
   context 'a token with two segments but does not require verifying' do
     it 'raises something else than "Not enough or too many segments"' do
-      expect { JWT.decode('ThisIsNotAValidJWTToken.second', nil, false) }.to raise_error(JWT::DecodeError, 'Invalid segment encoding')
+      expect { JWT.decode('ThisIsNotAValidJWTToken.second', nil, false) }.to raise_error(JWT::Base64DecodeError, 'Invalid base64 encoding')
     end
   end
 
@@ -736,8 +736,8 @@
 
   context 'when token ends with a newline char' do
     let(:token) { "#{JWT.encode(payload, 'secret', 'HS256')}\n" }
-    it 'ignores the newline and decodes the token' do
-      expect(JWT.decode(token, 'secret', true, algorithm: 'HS256')).to include(payload)
+    it 'raises an error' do
+      expect { JWT.decode(token, 'secret', true, algorithm: 'HS256') }.to raise_error(JWT::Base64DecodeError, 'Invalid base64 encoding')
     end
   end
 
@@ -949,34 +949,4 @@ def verify(*)
       end
     end
   end
-
-  context 'when invalid token is valid loose base64' do
-    it 'does not output deprecations warnings' do
-      expect do
-        JWT.decode("#{JWT.encode('a', 'b')} 9", 'b')
-      rescue JWT::VerificationError
-        nil
-      end.not_to output(/DEPRECATION/).to_stderr
-    end
-  end
-
-  context 'when valid token is invalid strict base64 and decoded with the correct key' do
-    it 'does outputs deprecation warning' do
-      expect { JWT.decode("#{JWT.encode('payload', 'key')} ", 'key') }.to output(/DEPRECATION/).to_stderr
-    end
-  end
-
-  context 'when valid token is invalid strict base64 and decoded with the incorrect key' do
-    it 'does not output deprecation warning, even when decoded with the correct key' do
-      token = JWT.encode('payload', 'key')
-      expect do
-        begin
-          JWT.decode("#{token} ", 'incorrect')
-        rescue JWT::VerificationError
-          nil
-        end
-        JWT.decode(token, 'key')
-      end.not_to output(/DEPRECATION/).to_stderr
-    end
-  end
 end