diff --git a/app/gui/themes.c b/app/gui/themes.c
index 73cb6b1c4b..09d07fa078 100644
--- a/app/gui/themes.c
+++ b/app/gui/themes.c
@@ -493,20 +493,17 @@ themes_apply_theme (Gimp          *gimp,
 
       if (! error && config->font_relative_size != 1.0)
         {
-          /* CSS does not like numbers with commas as the radix.
-           * To prevent, we create the string with a point used. */
-          gchar *font_size_string = NULL;
-          gint   font_size;
-
-          font_size = config->font_relative_size * 100;
-          font_size_string = g_strdup_printf ("%d.%d", (font_size / 100),
-                                              font_size % 100);
+          /* Intermediate buffer for locale-independent float to string
+           * conversion. See issue #11048.
+           */
+          gchar font_size_string[G_ASCII_DTOSTR_BUF_SIZE];
 
           g_output_stream_printf (output, NULL, NULL, &error,
                                   "\n"
                                   "* { font-size: %srem; }",
-                                  font_size_string);
-          g_free (font_size_string);
+                                  g_ascii_dtostr (font_size_string,
+                                                  G_ASCII_DTOSTR_BUF_SIZE,
+                                                  config->font_relative_size));
         }
 
       if (! error)