diff --git a/src/silx/gui/plot/backends/BackendOpenGL.py b/src/silx/gui/plot/backends/BackendOpenGL.py
index b8614c8d3d..7bdba1b80d 100755
--- a/src/silx/gui/plot/backends/BackendOpenGL.py
+++ b/src/silx/gui/plot/backends/BackendOpenGL.py
@@ -912,7 +912,7 @@ def _lineStyleToDashOffsetPattern(
             pattern = ()
         if len(pattern) == 2:
             pattern = pattern * 2
-        return offset, pattern
+        return float(offset), tuple(float(v) for v in pattern)
 
     def addCurve(
         self,