diff --git a/scripts/tests/e3a.lua b/scripts/tests/e3a.lua
index 0e8df42ba..ae9c0903d 100644
--- a/scripts/tests/e3a.lua
+++ b/scripts/tests/e3a.lua
@@ -416,6 +416,9 @@ function test_alliance()
   assert(f1.alliance~=nil)
   assert(f2.alliance~=nil)
   assert(f2.alliance==f1.alliance)
+  for f in f1.alliance.factions do
+    assert_true(f==f1 or f==f2)
+  end
   u1:clear_orders()
   u2:clear_orders()
   u2:add_order("ALLIANZ AUSSTOSSEN " .. itoa36(f1.id))
diff --git a/src/eressea.vcxproj b/src/eressea.vcxproj
index 9b2e3a9c0..923c88f6a 100644
--- a/src/eressea.vcxproj
+++ b/src/eressea.vcxproj
@@ -57,6 +57,7 @@
       <PrecompiledHeaderFile>stdafx.h</PrecompiledHeaderFile>
       <WarningLevel>Level4</WarningLevel>
       <DebugInformationFormat>EditAndContinue</DebugInformationFormat>
+      <TreatWarningAsError>true</TreatWarningAsError>
     </ClCompile>
     <Link>
       <AdditionalDependencies>libxml2.lib;pdcurses.lib;lua.lib;tolua.lib;ws2_32.lib;%(AdditionalDependencies)</AdditionalDependencies>
@@ -74,6 +75,7 @@
       <PrecompiledHeader>Use</PrecompiledHeader>
       <WarningLevel>Level3</WarningLevel>
       <DebugInformationFormat>ProgramDatabase</DebugInformationFormat>
+      <TreatWarningAsError>true</TreatWarningAsError>
     </ClCompile>
     <Link>
       <AdditionalDependencies>libxml2.lib;pdcurses.lib;lua.lib;tolua.lib;%(AdditionalDependencies)</AdditionalDependencies>