diff --git a/ClosedXML_Tests/ClosedXML_Tests.csproj b/ClosedXML_Tests/ClosedXML_Tests.csproj
index aae1fea..b830716 100644
--- a/ClosedXML_Tests/ClosedXML_Tests.csproj
+++ b/ClosedXML_Tests/ClosedXML_Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netcoreapp2.0;net461</TargetFrameworks>
+    <TargetFrameworks>netcoreapp2.0;net40;net461</TargetFrameworks>
     <IsPackable>false</IsPackable>
   </PropertyGroup>
 
diff --git a/appveyor.yml b/appveyor.yml
index c552385..0585b42 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -40,6 +40,6 @@
 
 test:
   assemblies:
-    only: 
-      - ClosedXML_Tests/bin/Release/netcoreapp2.0/ClosedXML_Tests.dll
-      - ClosedXML_Tests/bin/Release/net461/ClosedXML_Tests.dll
+    - ClosedXML_Tests/bin/Release/netcoreapp2.0/ClosedXML_Tests.dll
+    - ClosedXML_Tests/bin/Release/net40/ClosedXML_Tests.dll
+    - ClosedXML_Tests/bin/Release/net461/ClosedXML_Tests.dll