diff --git a/plugins/LegacyProfileReader/DictionaryOfDoom.json b/plugins/LegacyProfileReader/DictionaryOfDoom.json
index 1fe7d7b7a5..8c4b49074b 100644
--- a/plugins/LegacyProfileReader/DictionaryOfDoom.json
+++ b/plugins/LegacyProfileReader/DictionaryOfDoom.json
@@ -50,7 +50,7 @@
         "skirt_minimal_length": "skirt_minimal_length",
         "brim_line_count": "brim_line_count",
         "raft_margin": "raft_margin",
-        "raft_airgap": "raft_airgap_all - raft_airgap",
+        "raft_airgap": "float(raft_airgap_all) - float(raft_airgap)",
         "layer_0_z_overlap": "raft_airgap",
         "raft_surface_layers": "raft_surface_layers",
         "raft_surface_thickness": "raft_surface_thickness",