diff --git a/ClosedXML_Tests/ClosedXML_Tests.csproj b/ClosedXML_Tests/ClosedXML_Tests.csproj
index 4276d00..58ae3fe 100644
--- a/ClosedXML_Tests/ClosedXML_Tests.csproj
+++ b/ClosedXML_Tests/ClosedXML_Tests.csproj
@@ -22,7 +22,7 @@
     <DebugType>full</DebugType>
     <Optimize>false</Optimize>
     <OutputPath>bin\Debug\</OutputPath>
-    <DefineConstants>DEBUG;TRACE</DefineConstants>
+    <DefineConstants>DEBUG;TRACE;$(AppVeyor)</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
@@ -30,7 +30,7 @@
     <DebugType>pdbonly</DebugType>
     <Optimize>true</Optimize>
     <OutputPath>bin\Release\</OutputPath>
-    <DefineConstants>TRACE</DefineConstants>
+    <DefineConstants>TRACE;$(AppVeyor)</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
   </PropertyGroup>
diff --git a/appveyor.yml b/appveyor.yml
index 16d9a67..469c8b6 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -9,6 +9,8 @@
     - gh-pages
 # Build worker image (VM template)
 image: Visual Studio 2015
+environment:
+  AppVeyor: APPVEYOR
 
 # enable patching of AssemblyInfo.* files
 assembly_info:
@@ -17,7 +19,7 @@
   assembly_version: "{version}"
   assembly_file_version: "{version}"
   assembly_informational_version: "{version}"
-  
+
 #---------------------------------#
 #       build configuration       #
 #---------------------------------#
@@ -29,10 +31,10 @@
   parallel: true                                            # enable MSBuild parallel builds
   project: ClosedXML.sln       # path to Visual Studio solution or project
   verbosity: minimal
- 
+
 configuration : Release
 
 #Restore
 before_build:
   - nuget restore
-  
+