diff --git a/sdc/Sdc.tcl b/sdc/Sdc.tcl
index f538bcfd..75b4b813 100644
--- a/sdc/Sdc.tcl
+++ b/sdc/Sdc.tcl
@@ -72,6 +72,9 @@ proc source_ { filename echo verbose } {
   if [catch {open $filename r} stream] {
     sta_error 340 "cannot open '$filename'."
   } else {
+    if { [info commands zlib] == "" } {
+      sta_error 339 "tcl version > 8.6 required for zlib support."
+    }
     if { [file extension $filename] == ".gz" } {
       zlib push gunzip $stream
     }