diff --git a/Source/cmNinjaTargetGenerator.cxx b/Source/cmNinjaTargetGenerator.cxx
index 7d3962a4a..6ae45a931 100644
--- a/Source/cmNinjaTargetGenerator.cxx
+++ b/Source/cmNinjaTargetGenerator.cxx
@@ -135,23 +135,8 @@ cmNinjaTargetGenerator::ComputeFlagsForObject(cmSourceFile const* source,
     this->LocalGenerator->AddVisibilityPresetFlags(languageFlags, this->Target,
                                                    language);
 
-    std::vector<std::string> includes;
-    this->LocalGenerator->GetIncludeDirectories(includes,
-                                                this->GeneratorTarget,
-                                                language,
-                                                this->GetConfigName());
     // Add include directory flags.
-    std::string includeFlags =
-      this->LocalGenerator->GetIncludeFlags(includes, this->GeneratorTarget,
-                                            language,
-      language == "RC" ? true : false,  // full include paths for RC
-                                        // needed by cmcldeps
-                                            false,
-                                            this->GetConfigName());
-    if (this->GetGlobalGenerator()->IsGCCOnWindows())
-      cmSystemTools::ReplaceString(includeFlags, "\\", "/");
-
-    this->LocalGenerator->AppendFlags(languageFlags, includeFlags);
+    this->AddIncludeFlags(languageFlags, language);
 
     // Append old-style preprocessor definition flags.
     this->LocalGenerator->AppendFlags(languageFlags,
@@ -180,6 +165,28 @@ cmNinjaTargetGenerator::ComputeFlagsForObject(cmSourceFile const* source,
   return flags;
 }
 
+void cmNinjaTargetGenerator::AddIncludeFlags(std::string& languageFlags,
+                                             std::string const& language)
+{
+  std::vector<std::string> includes;
+  this->LocalGenerator->GetIncludeDirectories(includes,
+                                              this->GeneratorTarget,
+                                              language,
+                                              this->GetConfigName());
+  // Add include directory flags.
+  std::string includeFlags =
+    this->LocalGenerator->GetIncludeFlags(includes, this->GeneratorTarget,
+                                          language,
+        language == "RC" ? true : false,  // full include paths for RC
+                                          // needed by cmcldeps
+                                          false,
+                                          this->GetConfigName());
+  if (this->GetGlobalGenerator()->IsGCCOnWindows())
+    cmSystemTools::ReplaceString(includeFlags, "\\", "/");
+
+  this->LocalGenerator->AppendFlags(languageFlags, includeFlags);
+}
+
 bool cmNinjaTargetGenerator::NeedDepTypeMSVC(const std::string& lang) const
 {
   if (lang == "C" || lang == "CXX")
diff --git a/Source/cmNinjaTargetGenerator.h b/Source/cmNinjaTargetGenerator.h
index ae668dde4..0cd5e4876 100644
--- a/Source/cmNinjaTargetGenerator.h
+++ b/Source/cmNinjaTargetGenerator.h
@@ -81,6 +81,8 @@ protected:
   std::string ComputeFlagsForObject(cmSourceFile const* source,
                                     const std::string& language);
 
+  void AddIncludeFlags(std::string& flags, std::string const& lang);
+
   std::string ComputeDefines(cmSourceFile const* source,
                              const std::string& language);