diff --git a/clang/include/clang/AST/DeclTemplate.h b/clang/include/clang/AST/DeclTemplate.h
--- a/clang/include/clang/AST/DeclTemplate.h
+++ b/clang/include/clang/AST/DeclTemplate.h
@@ -3287,8 +3287,12 @@
     return isa<TemplateTypeParmDecl>(getTemplateParameters()->getParam(0));
   }
 
-  ConceptDecl *getCanonicalDecl() override { return getFirstDecl(); }
-  const ConceptDecl *getCanonicalDecl() const { return getFirstDecl(); }
+  ConceptDecl *getCanonicalDecl() override {
+    return cast<ConceptDecl>(getPrimaryMergedDecl(this));
+  }
+  const ConceptDecl *getCanonicalDecl() const {
+    return const_cast<ConceptDecl *>(this)->getCanonicalDecl();
+  }
 
   // Implement isa/cast/dyncast/etc.
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
diff --git a/clang/test/Modules/merge-concepts.cpp b/clang/test/Modules/merge-concepts.cpp
--- a/clang/test/Modules/merge-concepts.cpp
+++ b/clang/test/Modules/merge-concepts.cpp
@@ -47,7 +47,10 @@
 #define SAME_AS_H
 
 template <class T, class U>
-concept same_as = __is_same(T, U);
+concept same_as_impl = __is_same(T, U);
+
+template <class T, class U>
+concept same_as = same_as_impl<T, U> && same_as_impl<U, T>;
 
 #endif // SAME_AS_H
 
@@ -55,11 +58,11 @@
 #ifndef FORMAT_H
 #define FORMAT_H
 
-#include "concepts.h"
 #include "same_as.h"
+#include "concepts.h"
 
 template <class T> void foo()
   requires same_as<T, int>
 {}
 
-#endif // FORMAT_H
\ No newline at end of file
+#endif // FORMAT_H