diff --git a/Lib/fontTools/varLib/iup.py b/Lib/fontTools/varLib/iup.py
index 41be6ba4f..9ff6c0eca 100644
--- a/Lib/fontTools/varLib/iup.py
+++ b/Lib/fontTools/varLib/iup.py
@@ -74,7 +74,14 @@ def iup_segment(
                 d = d2
             else:
                 # Interpolate
-                d = d1 + (x - x1) * scale
+                #
+                # NOTE: we assign an explicit intermediate variable here in
+                # order to disable a fused mul-add optimization. See:
+                #
+                # - https://godbolt.org/z/YsP4T3TqK,
+                # - https://github.com/fonttools/fonttools/issues/3703
+                nudge = (x - x1) * scale
+                d = d1 + nudge
 
             out.append(d)