diff --git a/lib/datadog/appsec/contrib/rack/gateway/request.rb b/lib/datadog/appsec/contrib/rack/gateway/request.rb
index b204894a537..86513a697a2 100644
--- a/lib/datadog/appsec/contrib/rack/gateway/request.rb
+++ b/lib/datadog/appsec/contrib/rack/gateway/request.rb
@@ -25,11 +25,13 @@ def request
             def query
               # Downstream libddwaf expects keys and values to be extractable
               # separately so we can't use [[k, v], ...]. We also want to allow
-              # duplicate keys, so we use [{k, v}, ...] instead.
-              request.query_string.split('&').map do |e|
+              # duplicate keys, so we use {k => [v, ...], ...} instead, taking into
+              # account that {k => [v1, v2, ...], ...} is possible for duplicate keys.
+              request.query_string.split('&').each.with_object({}) do |e, hash|
                 k, v = e.split('=').map { |s| CGI.unescape(s) }
+                hash[k] ||= []
 
-                { k => v }
+                hash[k] << v
               end
             end
 
diff --git a/spec/datadog/appsec/contrib/rack/gateway/request_spec.rb b/spec/datadog/appsec/contrib/rack/gateway/request_spec.rb
index 9ee4d422525..495ef2fbb0b 100644
--- a/spec/datadog/appsec/contrib/rack/gateway/request_spec.rb
+++ b/spec/datadog/appsec/contrib/rack/gateway/request_spec.rb
@@ -8,7 +8,7 @@
   let(:request) do
     described_class.new(
       Rack::MockRequest.env_for(
-        'http://example.com:8080/?a=foo',
+        'http://example.com:8080/?a=foo&a=bar&b=baz',
         {
           'REQUEST_METHOD' => 'GET', 'REMOTE_ADDR' => '10.10.10.10', 'HTTP_CONTENT_TYPE' => 'text/html',
           'HTTP_COOKIE' => 'foo=bar', 'HTTP_USER_AGENT' => 'WebKit'
@@ -19,7 +19,7 @@
 
   describe '#query' do
     it 'returns URL query information' do
-      expect(request.query).to eq([{ 'a' => 'foo' }])
+      expect(request.query).to eq({ 'a' => ['foo', 'bar'], 'b' => ['baz'] })
     end
   end
 
@@ -38,7 +38,7 @@
 
   describe '#url' do
     it 'returns the url' do
-      expect(request.url).to eq('http://example.com:8080/?a=foo')
+      expect(request.url).to eq('http://example.com:8080/?a=foo&a=bar&b=baz')
     end
   end
 
@@ -50,7 +50,7 @@
 
   describe '#fullpath' do
     it 'returns the path with query string' do
-      expect(request.fullpath).to eq('/?a=foo')
+      expect(request.fullpath).to eq('/?a=foo&a=bar&b=baz')
     end
   end
 
diff --git a/spec/datadog/appsec/contrib/rack/reactive/request_spec.rb b/spec/datadog/appsec/contrib/rack/reactive/request_spec.rb
index 507a585c077..c30f9e4301a 100644
--- a/spec/datadog/appsec/contrib/rack/reactive/request_spec.rb
+++ b/spec/datadog/appsec/contrib/rack/reactive/request_spec.rb
@@ -20,7 +20,7 @@
   describe '.publish' do
     it 'propagates request attributes to the operation' do
       expect(operation).to receive(:publish).with('server.request.method', 'GET')
-      expect(operation).to receive(:publish).with('request.query', [{ 'a' => 'foo' }])
+      expect(operation).to receive(:publish).with('request.query', { 'a' => ['foo'] })
       expect(operation).to receive(:publish).with('request.headers', { 'content-type' => 'text/html' })
       expect(operation).to receive(:publish).with('request.uri.raw', '/?a=foo')
       expect(operation).to receive(:publish).with('request.cookies', {})
@@ -53,7 +53,7 @@
 
         expected_waf_arguments = {
           'server.request.cookies' => {},
-          'server.request.query' => [{ 'a' => 'foo' }],
+          'server.request.query' => { 'a' => ['foo'] },
           'server.request.uri.raw' => '/?a=foo',
           'server.request.headers' => { 'content-type' => 'text/html' },
           'server.request.headers.no_cookies' => { 'content-type' => 'text/html' },