diff --git a/premake5.lua b/premake5.lua
index 9c6d8e2f..a8c1d4b2 100644
--- a/premake5.lua
+++ b/premake5.lua
@@ -25,7 +25,7 @@ newaction {
 		if oldVersionHeader ~=nil then
 			local oldVersionHeaderContent = assert(oldVersionHeader:read('*a'))
 			oldRevNumber = string.match(oldVersionHeaderContent, "#define REVISION (%d+)")
-			if oldRevNumber = nil then
+			if oldRevNumber == nil then
 				-- old version.hpp format?
 				oldRevNumber = "(none)"
 			end