diff --git a/cmake/QtIRCommandLineHelpers.cmake b/cmake/QtIRCommandLineHelpers.cmake
index b932fcdf..8856e980 100644
--- a/cmake/QtIRCommandLineHelpers.cmake
+++ b/cmake/QtIRCommandLineHelpers.cmake
@@ -427,11 +427,13 @@ endfunction()
 # Convert to absolute path if necessary.
 function(qt_ir_get_option_as_existing_absolute_path name value)
     qt_ir_get_option_value("${name}" path)
-    if(NOT EXISTS "${abspath}")
-        qt_ir_add_error("The path '${path}' passed with -${name} does not exist.")
-    endif()
-    if(NOT IS_ABSOLUTE "${path}")
-        get_filename_component(path "${path}" ABSOLUTE)
+    if(NOT "${path}" STREQUAL "")
+        if(NOT EXISTS "${path}")
+            qt_ir_add_error("The path '${path}' passed with -${name} does not exist.")
+        endif()
+        if(NOT IS_ABSOLUTE "${path}")
+            get_filename_component(path "${path}" ABSOLUTE)
+        endif()
     endif()
     set("${value}" "${path}" PARENT_SCOPE)
 endfunction()