diff --git a/sdc/Sdc.tcl b/sdc/Sdc.tcl
index ed568f8b..112ea504 100644
--- a/sdc/Sdc.tcl
+++ b/sdc/Sdc.tcl
@@ -144,11 +144,11 @@ proc check_unit { unit key suffix key_var } {
     set arg_suffix [string range $value end-[expr $suffix_length - 1] end]
     if { [string match -nocase $arg_suffix $suffix] } {
       set arg_prefix [string range $value 0 end-$suffix_length]
-      if { [regexp "^(10*\.?0*)?(\[Mkmunpf\])?$" $arg_prefix ignore mult prefix] } {
+      if { [regexp "^(10*\\\.?0*)?(\[Mkmunpf\])?$" $arg_prefix ignore mult prefix] } {
         if { $mult == "" } {
           set mult 1
         }
-        set scale [unit_prefix_scale $unit $prefix ]
+        set scale [unit_prefix_scale $unit $prefix]
         check_unit_scale $unit [expr $scale * $mult]
       } else {
         sta_error 343 "unknown unit $unit prefix '${arg_prefix}'."