diff --git a/css/theme/irstea.css b/css/theme/irstea.css
index fbf0873499ef217af2f0c5d5416e0c9ed2928419..d81b1684a5028b878275fd64593521ba2c69bb8c 100644
--- a/css/theme/irstea.css
+++ b/css/theme/irstea.css
@@ -279,7 +279,7 @@ body {
   .reveal .slides .date {
     color: #9293a1;
     font-variant: small-caps; }
-  .reveal .slides section:not(:first-child) {
+  .reveal .slides section:not(:first-child):not(.stack) {
     background: top left url(../../lib/images/prairie-petit.png) no-repeat;
     padding: 75px 0 0 75px;
     margin-top: -10px;
diff --git a/css/theme/source/irstea.scss b/css/theme/source/irstea.scss
index 2bd77061cffaa8184548a11ea5e9a11f667cc4b2..477f50cb00b11db3e618e1b6d3a83bbe41553e4c 100644
--- a/css/theme/source/irstea.scss
+++ b/css/theme/source/irstea.scss
@@ -57,7 +57,7 @@ $selectionColor: #fff;
       font-variant: small-caps;
     }
 
-    section:not(:first-child) {
+    section:not(:first-child):not(.stack) {
       background: top left url(../../lib/images/prairie-petit.png) no-repeat;
       padding: 75px 0 0 75px;
       margin-top: -10px;