diff --git a/AlgebraicDataflowArchitectureModel/src/code/ast/NumberUtil.java b/AlgebraicDataflowArchitectureModel/src/code/ast/NumberUtil.java
index 7d07105..dd076e8 100644
--- a/AlgebraicDataflowArchitectureModel/src/code/ast/NumberUtil.java
+++ b/AlgebraicDataflowArchitectureModel/src/code/ast/NumberUtil.java
@@ -16,7 +16,7 @@
 	 * @return {@code true} if the given string represents a valid hexadecimal number,
 	 * {@code false} otherwise.
 	 * @apiNote This method returns {@code true} if the given token is a valid hexadecimal number representaion in <b>Java source code</b>.
-	 * So make sure that the specification of this method is determined by Java language specification.
+	 * So make sure that the specification of this method is determined by Java language specification. Hexadecimal Floating-Point is not supported yet.
 	 */
 	public static boolean isHexNumber(String token) {
 		if (token == null) {
@@ -42,14 +42,38 @@
 			return false;
 		}
 		
-		char prev = lexer.peek();
+		char prev = 'x'; // Prior character is 'x'
+		boolean hasDigit = false;
+		
 		while (lexer.peek() != '\0') {
 			char c = lexer.advance();
-			boolean isValidFormat = (c >= '0' && c <= '9') || (c >= 'a' && c <= 'f') || (c == '_');
+			
+			if (c == 'l') {
+				// Suffix for long literal must be the last character in the literal.
+				if (lexer.peek() != '\0') {
+					return false;
+				}
+				
+				// Suffix must NOT be located right after an underscore
+				if (prev == '_') {
+					return false;
+				}
+				
+				// Finish checking the format
+				break;
+			}
+			
+			boolean isDigit = (c >= '0' && c <= '9') || (c >= 'a' && c <= 'f');
+			boolean isValidFormat = isDigit || (c == '_');
+			
 			if (!isValidFormat) {
 				return false;
 			}
 			
+			if (isDigit) {
+				hasDigit = true;
+			}
+			
 			// Save the previous character
 			prev = c;
 		}
@@ -59,6 +83,10 @@
 			return false;
 		}
 		
+		if (!hasDigit) {
+			return false;
+		}
+		
 		return true;
 	}
 }