diff --git a/config/regex.txt b/config/regex.txt
index 35f5cc9..c4117f1 100644
--- a/config/regex.txt
+++ b/config/regex.txt
@@ -2,7 +2,7 @@
 
 # Year start
 ^(?<year>
-    (?<yearOpenFlag>[~?%]{0,2})
+    (?<yearOpenFlag>[~?%]{0,1})
     Y?
     (?<yearNum>
         [+-]?               # optional sign
@@ -14,7 +14,7 @@
     (?>S                    # Literal S letter. It is for the significant digit indicator
         (?<yearSignificantDigit>\d+)
 	)?
-    (?<yearCloseFlag>\)?[~%?]{0,2})
+    (?<yearCloseFlag>\)?[~%?]{0,1})
 )
 # Year end
 
@@ -22,24 +22,24 @@
 
     # Month start
     (?<month>
-        (?<monthOpenFlag>[~?%]{0,2})
+        (?<monthOpenFlag>[~?%]{0,1})
         (?<monthOpenParents>\(+)?
         (?<monthNum>(?>1[0-9UX]|[0UX][0-9UX]|[0-9][0-9]))
         (?>\^(?<seasonQualifier>[\P{L}\P{N}\P{M}:.-]+))?
-        (?<monthCloseFlag>[~?%]{0,2})
+        (?<monthCloseFlag>[~?%]{0,1})
     )
     # Month end
 
     (?>- # Begin Day Literal - (hyphen)
         # Day start
         (?<day>
-            (?<dayOpenFlag>[~?%]{0,2})
+            (?<dayOpenFlag>[~?%]{0,1})
             (?<dayOpenParents>\(+)?
                 (?<dayNum>
                     (?>[012UX][0-9UX]|3[01UX])
                 )
             )
-            (?<dayCloseFlag>[~?%]{0,2})
+            (?<dayCloseFlag>[~?%]{0,1})
             (?<dayEnd>[)~%?]*)
         # Day end
 
diff --git a/src/PackagePrivate/Parser/Parser.php b/src/PackagePrivate/Parser/Parser.php
index f6de06f..64ca248 100644
--- a/src/PackagePrivate/Parser/Parser.php
+++ b/src/PackagePrivate/Parser/Parser.php
@@ -209,7 +209,10 @@ private function buildQualification(): Qualification {
 
 	// TODO
 	private static function genQualificationValue( ?string $flag = null ): int {
-		assert( is_string( $flag ) );
+		if ( !is_string( $flag ) || !array_key_exists( $flag, self::$map ) ) {
+			throw new InvalidArgumentException( 'Qualifier is invalid' );
+		}
+
 		return (int)self::$map[$flag];
 	}
 
diff --git a/tests/Unit/PackagePrivate/Parser/ParserTest.php b/tests/Unit/PackagePrivate/Parser/ParserTest.php
index 922959d..a530d03 100644
--- a/tests/Unit/PackagePrivate/Parser/ParserTest.php
+++ b/tests/Unit/PackagePrivate/Parser/ParserTest.php
@@ -292,4 +292,27 @@ public function setOpenMiddleNonExtDateValues(): array {
 			[ "{2000%..2000-02}", "Dates in set ranges cannot be uncertain" ],
 		];
 	}
+
+	/**
+	 * @dataProvider provideCombinedUncertainAndApproximateQualifiers
+	 */
+	public function testThrowExceptionWhenUsedCombinedUncertainAndApproximateQualifiers( string $combinedUncertainAndApproximate ): void {
+		$parser = new Parser();
+		$this->expectException( InvalidArgumentException::class );
+		$this->expectExceptionMessage( 'Invalid edtf format ' . $combinedUncertainAndApproximate );
+		$parser->createEdtf( $combinedUncertainAndApproximate );
+	}
+
+	public function provideCombinedUncertainAndApproximateQualifiers(): array {
+		return [
+			[ '1990?~' ],
+			[ '1990~?' ],
+			[ '?~1990}' ],
+			[ '~?1990' ],
+			[ '1990-02~?' ],
+			[ '1990-?~02' ],
+			[ '1990-?~02~?-03' ],
+			[ '1990-02-~?03' ],
+		];
+	}
 }
\ No newline at end of file