diff --git a/.gitignore b/.gitignore
index 4a27759..e149be6 100644
--- a/.gitignore
+++ b/.gitignore
@@ -16,4 +16,4 @@ cabal.sandbox.config
 *.prof
 *.aux
 *.hp
-.stack-work/
+.stack-work/
\ No newline at end of file
diff --git a/src/Data/Swagger/Internal.hs b/src/Data/Swagger/Internal.hs
index 54dc7ee..4fd0efa 100644
--- a/src/Data/Swagger/Internal.hs
+++ b/src/Data/Swagger/Internal.hs
@@ -920,6 +920,18 @@ instance OVERLAPPING_ SwaggerMonoid (InsOrdHashMap FilePath PathItem) where
   swaggerMempty = InsOrdHashMap.empty
   swaggerMappend = InsOrdHashMap.unionWith mappend
 
+instance OVERLAPPING_ SwaggerMonoid (InsOrdHashMap Text SecurityScheme) where
+  swaggerMempty = InsOrdHashMap.empty
+  swaggerMappend = InsOrdHashMap.unionWith mergeFun
+    where
+      mergeFun s1@(SecurityScheme (SecuritySchemeOAuth2 (OAuth2Params flow1 scopes1)) desc)
+               s2@(SecurityScheme (SecuritySchemeOAuth2 (OAuth2Params flow2 scopes2)) _)
+        = if flow1 == flow2 then
+            SecurityScheme (SecuritySchemeOAuth2 (OAuth2Params flow1 (scopes1 <> scopes2))) desc
+          else
+            s2
+      mergeFun _ ss = ss
+
 instance Monoid a => SwaggerMonoid (Referenced a) where
   swaggerMempty = Inline mempty
   swaggerMappend (Inline x) (Inline y) = Inline (mappend x y)