diff --git a/lib/Slic3r/Config.pm b/lib/Slic3r/Config.pm
index 34738e5b5..81af8d9e6 100644
--- a/lib/Slic3r/Config.pm
+++ b/lib/Slic3r/Config.pm
@@ -168,8 +168,9 @@ sub validate {
         if $self->first_layer_height !~ /^(?:\d*(?:\.\d+)?)%?$/;
     die "Invalid value for --first-layer-height\n"
         if $self->get_value('first_layer_height') <= 0;
-    die "Adaptive slicing requires a non-relative first layer height."
-        if $self->get_value('adaptive_slicing') && $self->first_layer_height ~= /^(?:\d*(?:\.\d+)?)%$/;
+
+    die "Adaptive slicing requires a non-relative first layer height.\n"
+        if $self->get_value('adaptive_slicing') == 1 and $self->first_layer_height =~ /^(?:\d*(?:\.\d+)?)%?$/;
     
     # --filament-diameter
     die "Invalid value for --filament-diameter\n"