diff --git a/docs/libcurl/symbols.pl b/docs/libcurl/symbols.pl
index 1105ae66b6..1751a4887d 100755
--- a/docs/libcurl/symbols.pl
+++ b/docs/libcurl/symbols.pl
@@ -44,12 +44,15 @@
 # #endif
 #
 #
+use strict;
+use warnings;
+
 open F, "<symbols-in-versions";
 
 sub str2num {
     my ($str)=@_;
-    if($str =~ /([0-9]*)\.([0-9]*)\.*([0-9]*)/) {
-        return sprintf("0x%06x", $1<<16 | $2 << 8 | $3);
+    if($str && $str =~ /([0-9]*)\.([0-9]*)\.*([0-9]*)/) {
+        return sprintf("0x%06x", $1 <<16 | $2 << 8 | ($3 || '0'));
     }
 }