diff --git a/common/src/main/java/org/opensearch/sql/common/grok/GrokCompiler.java b/common/src/main/java/org/opensearch/sql/common/grok/GrokCompiler.java
index aba96ad4cb..05fdbd57ed 100644
--- a/common/src/main/java/org/opensearch/sql/common/grok/GrokCompiler.java
+++ b/common/src/main/java/org/opensearch/sql/common/grok/GrokCompiler.java
@@ -29,7 +29,7 @@
 public class GrokCompiler implements Serializable {
 
   // We don't want \n and commented line
-  private static final Pattern patternLinePattern = Pattern.compile("^([A-z0-9_]+)\\s+(.*)$");
+  private static final Pattern patternLinePattern = Pattern.compile("^([a-zA-Z0-9_]+)\\s+(.*)$");
 
   /** {@code Grok} patterns definitions. */
   private final Map<String, String> grokPatternDefinitions = new HashMap<>();
diff --git a/common/src/main/java/org/opensearch/sql/common/grok/GrokUtils.java b/common/src/main/java/org/opensearch/sql/common/grok/GrokUtils.java
index 4b145bbbe8..2a309bba8f 100644
--- a/common/src/main/java/org/opensearch/sql/common/grok/GrokUtils.java
+++ b/common/src/main/java/org/opensearch/sql/common/grok/GrokUtils.java
@@ -24,8 +24,8 @@ public class GrokUtils {
       Pattern.compile(
           "%\\{"
               + "(?<name>"
-              + "(?<pattern>[A-z0-9]+)"
-              + "(?::(?<subname>[A-z0-9_:;,\\-\\/\\s\\.']+))?"
+              + "(?<pattern>[a-zA-Z0-9_]+)"
+              + "(?::(?<subname>[a-zA-Z0-9_:;,\\-\\/\\s\\.']+))?"
               + ")"
               + "(?:=(?<definition>"
               + "(?:"