diff --git a/latex/yssymbols.sty b/latex/yssymbols.sty
index 933a58b..3f1c2e7 100644
--- a/latex/yssymbols.sty
+++ b/latex/yssymbols.sty
@@ -74,8 +74,9 @@
 \let\ensquot\faktor
 
 \def\ssitext{\@ifnextchar i{si et seulement s'}{si et seulement si\xspace}}
-\def\ssimath{\text{ s.s.i }}
-\def\ssi{\ifmmode\ssimath\else\ssitext\fi}
+\def\ssimath{\mathrel{\text{ s.s.i }}}
+\def\ssi{\ifmmode\let\next\ssimath\else\let\next\ssitext\fi\next}
+
 \RequirePackage{relsize}
 \DeclareRobustCommand\mention[1]{\texorpdfstring{\tikz[baseline=(char.base)]{
         \node[shape=rectangle, rounded corners,draw,inner sep=2pt] (char) {\textsmaller{#1}};}}{(#1)}}