diff --git a/Contrib/MultiUser/MultiUser.nsh b/Contrib/MultiUser/MultiUser.nsh
index 38cb5e31..ee95c758 100644
--- a/Contrib/MultiUser/MultiUser.nsh
+++ b/Contrib/MultiUser/MultiUser.nsh
@@ -36,9 +36,13 @@ Var MultiUser.InstallMode
     !insertmacro un.GetParameters
   !endif
   !include StrFunc.nsh
-  ${StrStr}
+  !ifndef StrStr_INCLUDED
+    ${StrStr}
+  !endif
   !ifndef MULTIUSER_NOUNINSTALL
-    ${UnStrStr}
+    !ifndef UnStrStr_INCLUDED
+      ${UnStrStr}
+    !endif
   !endif
   
   Var MultiUser.Parameters
diff --git a/Include/StrFunc.nsh b/Include/StrFunc.nsh
index 7a106ed4..ed3b8cdd 100644
--- a/Include/StrFunc.nsh
+++ b/Include/StrFunc.nsh
@@ -85,12 +85,14 @@ o-----------------------------------------------------------------------------o
       !echo `${STRFUNC_FUNCMSGPRE}$ {Un${ShortName}} - © ${Credits}${STRFUNC_FUNCMSGPOST}`
       !verbose pop
       !define `Un${ShortName}` `!insertmacro FUNCTION_STRING_Un${ShortName}_Call`
+      !define `Un${ShortName}_INCLUDED`
       Function `un.${ShortName}`
     !else
       !echo `${STRFUNC_FUNCMSGPRE}$ {${ShortName}} - © ${Credits}${STRFUNC_FUNCMSGPOST}`
       !verbose pop
       !undef `${ShortName}`
       !define `${ShortName}` `!insertmacro FUNCTION_STRING_${ShortName}_Call`
+      !define `${ShortName}_INCLUDED`
       Function `${ShortName}`
     !endif
   !macroend