diff --git a/src/backends.jl b/src/backends.jl
index 6a5dea31..9a5a7e1c 100644
--- a/src/backends.jl
+++ b/src/backends.jl
@@ -149,7 +149,7 @@ function pickDefaultBackend()
                 @warn("You have set `PLOTS_DEFAULT_BACKEND=$env_default` but `$(backend_package_name(sym))` is not loaded.")
             end
         else
-            @warn("You have set PLOTS_DEFAULT_BACKEND=$env_default but it is not a valid backend package.  Choose from:\n\t",
+            @warn("You have set PLOTS_DEFAULT_BACKEND=$env_default but it is not a valid backend package.  Choose from:\n\t" *
                  join(sort(_backends), "\n\t"))
         end
     end