diff --git a/lib/Differentiator/BaseForwardModeVisitor.cpp b/lib/Differentiator/BaseForwardModeVisitor.cpp
index 2b67f940b..c6689ec6e 100644
--- a/lib/Differentiator/BaseForwardModeVisitor.cpp
+++ b/lib/Differentiator/BaseForwardModeVisitor.cpp
@@ -947,125 +947,6 @@ BaseForwardModeVisitor::VisitFloatingLiteral(const FloatingLiteral* FL) {
   return StmtDiff(Clone(FL), constant0);
 }
 
-// This method is derived from the source code of both
-// buildOverloadedCallSet() in SemaOverload.cpp
-// and ActOnCallExpr() in SemaExpr.cpp.
-bool DerivativeBuilder::noOverloadExists(Expr* UnresolvedLookup,
-                                         llvm::MutableArrayRef<Expr*> ARargs) {
-  if (UnresolvedLookup->getType() == m_Context.OverloadTy) {
-    OverloadExpr::FindResult find = OverloadExpr::find(UnresolvedLookup);
-
-    if (!find.HasFormOfMemberPointer) {
-      OverloadExpr* ovl = find.Expression;
-
-      if (isa<UnresolvedLookupExpr>(ovl)) {
-        ExprResult result;
-        SourceLocation Loc;
-        OverloadCandidateSet CandidateSet(Loc,
-                                          OverloadCandidateSet::CSK_Normal);
-        Scope* S = m_Sema.getScopeForContext(m_Sema.CurContext);
-        UnresolvedLookupExpr* ULE = cast<UnresolvedLookupExpr>(ovl);
-        // Populate CandidateSet.
-        m_Sema.buildOverloadedCallSet(S, UnresolvedLookup, ULE, ARargs, Loc,
-                                      &CandidateSet, &result);
-        OverloadCandidateSet::iterator Best;
-        OverloadingResult OverloadResult = CandidateSet.BestViableFunction(
-            m_Sema, UnresolvedLookup->getBeginLoc(), Best);
-        if (OverloadResult) // No overloads were found.
-          return true;
-      }
-    }
-  }
-  return false;
-}
-
-// FIXME: Move this to DerivativeBuilder.cpp
-Expr* DerivativeBuilder::BuildCallToCustomDerivativeOrNumericalDiff(
-    const std::string& Name, llvm::SmallVectorImpl<Expr*>& CallArgs,
-    clang::Scope* S, clang::DeclContext* originalFnDC,
-    bool forCustomDerv /*=true*/, bool namespaceShouldExist /*=true*/) {
-  NamespaceDecl* NSD = nullptr;
-  std::string namespaceID;
-  if (forCustomDerv) {
-    namespaceID = "custom_derivatives";
-    NamespaceDecl* cladNS = nullptr;
-    if (m_BuiltinDerivativesNSD)
-      NSD = m_BuiltinDerivativesNSD;
-    else {
-      cladNS = utils::LookupNSD(m_Sema, "clad", /*shouldExist=*/true);
-      NSD = utils::LookupNSD(m_Sema, namespaceID, namespaceShouldExist, cladNS);
-      m_BuiltinDerivativesNSD = NSD;
-    }
-  } else {
-    NSD = m_NumericalDiffNSD;
-    namespaceID = "numerical_diff";
-  }
-  if (!NSD) {
-    NSD = utils::LookupNSD(m_Sema, namespaceID, namespaceShouldExist);
-    if (!forCustomDerv && !NSD) {
-      diag(DiagnosticsEngine::Warning, noLoc,
-           "Numerical differentiation is diabled using the "
-           "-DCLAD_NO_NUM_DIFF "
-           "flag, this means that every try to numerically differentiate a "
-           "function will fail! Remove the flag to revert to default "
-           "behaviour.");
-      return nullptr;
-    }
-  }
-  CXXScopeSpec SS;
-  DeclContext* DC = NSD;
-
-  // FIXME: Here `if` branch should be removed once we update
-  // numerical diff to use correct declaration context.
-  if (forCustomDerv) {
-    DeclContext* outermostDC = utils::GetOutermostDC(m_Sema, originalFnDC);
-    // FIXME: We should ideally construct nested name specifier from the
-    // found custom derivative function. Current way will compute incorrect
-    // nested name specifier in some cases.
-    if (outermostDC &&
-        outermostDC->getPrimaryContext() == NSD->getPrimaryContext()) {
-      utils::BuildNNS(m_Sema, originalFnDC, SS);
-      DC = originalFnDC;
-    } else {
-      if (isa<RecordDecl>(originalFnDC))
-        DC = utils::LookupNSD(m_Sema, "class_functions",
-                              /*shouldExist=*/false, NSD);
-      else
-        DC = utils::FindDeclContext(m_Sema, NSD, originalFnDC);
-      if (DC)
-        utils::BuildNNS(m_Sema, DC, SS);
-    }
-  } else {
-    SS.Extend(m_Context, NSD, noLoc, noLoc);
-  }
-  IdentifierInfo* II = &m_Context.Idents.get(Name);
-  DeclarationName name(II);
-  DeclarationNameInfo DNInfo(name, utils::GetValidSLoc(m_Sema));
-
-  LookupResult R(m_Sema, DNInfo, Sema::LookupOrdinaryName);
-  if (DC)
-    m_Sema.LookupQualifiedName(R, DC);
-  Expr* OverloadedFn = 0;
-  if (!R.empty()) {
-    // FIXME: We should find a way to specify nested name specifier
-    // after finding the custom derivative.
-    Expr* UnresolvedLookup =
-        m_Sema.BuildDeclarationNameExpr(SS, R, /*ADL*/ false).get();
-
-    llvm::MutableArrayRef<Expr*> MARargs =
-        llvm::MutableArrayRef<Expr*>(CallArgs);
-
-    SourceLocation Loc;
-
-    if (noOverloadExists(UnresolvedLookup, MARargs))
-      return 0;
-
-    OverloadedFn =
-        m_Sema.ActOnCallExpr(S, UnresolvedLookup, Loc, MARargs, Loc).get();
-  }
-  return OverloadedFn;
-}
-
 QualType
 BaseForwardModeVisitor::GetPushForwardDerivativeType(QualType ParamType) {
   return ParamType;
diff --git a/lib/Differentiator/DerivativeBuilder.cpp b/lib/Differentiator/DerivativeBuilder.cpp
index 23417dfda..96db90302 100644
--- a/lib/Differentiator/DerivativeBuilder.cpp
+++ b/lib/Differentiator/DerivativeBuilder.cpp
@@ -134,6 +134,125 @@ namespace clad {
     return { returnedFD, enclosingNS };
   }
 
+  // This method is derived from the source code of both
+  // buildOverloadedCallSet() in SemaOverload.cpp
+  // and ActOnCallExpr() in SemaExpr.cpp.
+  bool
+  DerivativeBuilder::noOverloadExists(Expr* UnresolvedLookup,
+                                      llvm::MutableArrayRef<Expr*> ARargs) {
+    if (UnresolvedLookup->getType() == m_Context.OverloadTy) {
+      OverloadExpr::FindResult find = OverloadExpr::find(UnresolvedLookup);
+
+      if (!find.HasFormOfMemberPointer) {
+        OverloadExpr* ovl = find.Expression;
+
+        if (isa<UnresolvedLookupExpr>(ovl)) {
+          ExprResult result;
+          SourceLocation Loc;
+          OverloadCandidateSet CandidateSet(Loc,
+                                            OverloadCandidateSet::CSK_Normal);
+          Scope* S = m_Sema.getScopeForContext(m_Sema.CurContext);
+          auto* ULE = cast<UnresolvedLookupExpr>(ovl);
+          // Populate CandidateSet.
+          m_Sema.buildOverloadedCallSet(S, UnresolvedLookup, ULE, ARargs, Loc,
+                                        &CandidateSet, &result);
+          OverloadCandidateSet::iterator Best = nullptr;
+          OverloadingResult OverloadResult = CandidateSet.BestViableFunction(
+              m_Sema, UnresolvedLookup->getBeginLoc(), Best);
+          if (OverloadResult != 0U) // No overloads were found.
+            return true;
+        }
+      }
+    }
+    return false;
+  }
+
+  Expr* DerivativeBuilder::BuildCallToCustomDerivativeOrNumericalDiff(
+      const std::string& Name, llvm::SmallVectorImpl<Expr*>& CallArgs,
+      clang::Scope* S, clang::DeclContext* originalFnDC,
+      bool forCustomDerv /*=true*/, bool namespaceShouldExist /*=true*/) {
+    NamespaceDecl* NSD = nullptr;
+    std::string namespaceID;
+    if (forCustomDerv) {
+      namespaceID = "custom_derivatives";
+      NamespaceDecl* cladNS = nullptr;
+      if (m_BuiltinDerivativesNSD)
+        NSD = m_BuiltinDerivativesNSD;
+      else {
+        cladNS = utils::LookupNSD(m_Sema, "clad", /*shouldExist=*/true);
+        NSD =
+            utils::LookupNSD(m_Sema, namespaceID, namespaceShouldExist, cladNS);
+        m_BuiltinDerivativesNSD = NSD;
+      }
+    } else {
+      NSD = m_NumericalDiffNSD;
+      namespaceID = "numerical_diff";
+    }
+    if (!NSD) {
+      NSD = utils::LookupNSD(m_Sema, namespaceID, namespaceShouldExist);
+      if (!forCustomDerv && !NSD) {
+        diag(DiagnosticsEngine::Warning, noLoc,
+             "Numerical differentiation is diabled using the "
+             "-DCLAD_NO_NUM_DIFF "
+             "flag, this means that every try to numerically differentiate a "
+             "function will fail! Remove the flag to revert to default "
+             "behaviour.");
+        return nullptr;
+      }
+    }
+    CXXScopeSpec SS;
+    DeclContext* DC = NSD;
+
+    // FIXME: Here `if` branch should be removed once we update
+    // numerical diff to use correct declaration context.
+    if (forCustomDerv) {
+      DeclContext* outermostDC = utils::GetOutermostDC(m_Sema, originalFnDC);
+      // FIXME: We should ideally construct nested name specifier from the
+      // found custom derivative function. Current way will compute incorrect
+      // nested name specifier in some cases.
+      if (outermostDC &&
+          outermostDC->getPrimaryContext() == NSD->getPrimaryContext()) {
+        utils::BuildNNS(m_Sema, originalFnDC, SS);
+        DC = originalFnDC;
+      } else {
+        if (isa<RecordDecl>(originalFnDC))
+          DC = utils::LookupNSD(m_Sema, "class_functions",
+                                /*shouldExist=*/false, NSD);
+        else
+          DC = utils::FindDeclContext(m_Sema, NSD, originalFnDC);
+        if (DC)
+          utils::BuildNNS(m_Sema, DC, SS);
+      }
+    } else {
+      SS.Extend(m_Context, NSD, noLoc, noLoc);
+    }
+    IdentifierInfo* II = &m_Context.Idents.get(Name);
+    DeclarationName name(II);
+    DeclarationNameInfo DNInfo(name, utils::GetValidSLoc(m_Sema));
+
+    LookupResult R(m_Sema, DNInfo, Sema::LookupOrdinaryName);
+    if (DC)
+      m_Sema.LookupQualifiedName(R, DC);
+    Expr* OverloadedFn = nullptr;
+    if (!R.empty()) {
+      // FIXME: We should find a way to specify nested name specifier
+      // after finding the custom derivative.
+      Expr* UnresolvedLookup =
+          m_Sema.BuildDeclarationNameExpr(SS, R, /*ADL*/ false).get();
+
+      auto MARargs = llvm::MutableArrayRef<Expr*>(CallArgs);
+
+      SourceLocation Loc;
+
+      if (noOverloadExists(UnresolvedLookup, MARargs))
+        return nullptr;
+
+      OverloadedFn =
+          m_Sema.ActOnCallExpr(S, UnresolvedLookup, Loc, MARargs, Loc).get();
+    }
+    return OverloadedFn;
+  }
+
   void DerivativeBuilder::AddErrorEstimationModel(
       std::unique_ptr<FPErrorEstimationModel> estModel) {
     m_EstModel.push_back(std::move(estModel));