diff --git a/src/Tools/cdtypes/src/types/cdstring.rs b/src/Tools/cdtypes/src/types/cdstring.rs
index 5ee57d54..0f7e8d8a 100644
--- a/src/Tools/cdtypes/src/types/cdstring.rs
+++ b/src/Tools/cdtypes/src/types/cdstring.rs
@@ -36,7 +36,7 @@ impl CDStringValidator for DStringValidator {
         for chr in value {
             let chr = *chr as char;    
 
-            if !matches!(chr, '0'..='9' | 'A'..='Z' | '_') {
+            if !matches!(chr, '\x00' | '\x01' | '0'..='9' | 'A'..='Z' | '_') {
                 return Err(Error::GenericError(format!("{} not a valid d-character", chr)));
             }
         }