diff --git a/README.md b/README.md
index 92c09d0..fc17fa3 100644
--- a/README.md
+++ b/README.md
@@ -155,7 +155,7 @@ The SAS type (char/numeric) of the values is determined according to a set of ru
 
 * If the values are numeric, the SAS type is numeric
 * If the values are all string, the SAS type is character
-* If the values contain a single character (a-Z + underscore) AND a numeric, then the SAS type is numeric (with special missing values).  
+* If the values contain a single character (a-Z + underscore + .) AND a numeric, then the SAS type is numeric (with special missing values).  
 * `null` is set to either '.' or '' depending on the assigned or derived type per the above rules.  If entire column is `null` then the type will be numeric.
 
 The following table illustrates the formats applied to columns under various scenarios:
diff --git a/src/utils/convertToCsv.ts b/src/utils/convertToCsv.ts
index f6a1a5b..64c6988 100644
--- a/src/utils/convertToCsv.ts
+++ b/src/utils/convertToCsv.ts
@@ -125,7 +125,7 @@ export const convertToCSV = (
         if (value && !specialMissingValueRegExp.test(value)) {
           console.log(`🤖[value]🤖`, value)
           throw new Error(
-            'Special missing value can only be a single character from A to Z or _'
+            'Special missing value can only be a single character from A to Z or _ or .'
           )
         }