diff --git a/ptbposter/ptbposter-new-engines.clo b/ptbposter/ptbposter-new-engines.clo
index ac8413d51bf57529540c0c67aefc61ba19ce76f4..913b37264d2c2094b369a454108f58e793ff0c22 100644
--- a/ptbposter/ptbposter-new-engines.clo
+++ b/ptbposter/ptbposter-new-engines.clo
@@ -28,8 +28,9 @@
 \setmathfont{texgyrepagella-math.otf}[math-style=ISO,bold-style=ISO]
 \ifPTB@serif\else
   \renewcommand*\familydefault{\sfdefault}
-  \setmathfont[range=it]{texgyreheros-italic.otf} 
   \RequirePackage[usefilenames,weight=Regular]{firamath-otf}
+  \unimathsetup{partial=upright}
+  \setmathfont[range=it]{texgyreheros-italic.otf}
 \fi
 \RequirePackage{newunicodechar}
 \newunicodechar{^^^^202f}{\,}% 'NARROW NO-BREAK SPACE' (\u202F, 8239)