diff --git a/src/find/matchers/mod.rs b/src/find/matchers/mod.rs
index e35ebbbb..c4cef7d2 100644
--- a/src/find/matchers/mod.rs
+++ b/src/find/matchers/mod.rs
@@ -341,7 +341,11 @@ fn convert_arg_to_comparable_value_and_suffix(
     option_name: &str,
     value_as_string: &str,
 ) -> Result<(ComparableValue, String), Box<dyn Error>> {
-    let re = Regex::new(r"([-+]?)[-+]?(\d+)(.*)$")?;
+    // Anchor at the start so a non-numeric prefix like "x5c" is rejected instead
+    // of silently parsing the "5c" in the middle. After the comparison sign GNU
+    // accepts one more optional '+' (so "++5c" and "-+5c" are valid, but "+-5c"
+    // and "--5c" are not), which `\+?` reproduces.
+    let re = Regex::new(r"^([-+]?)\+?(\d+)(.*)$")?;
     if let Some(groups) = re.captures(value_as_string) {
         if let Ok(val) = groups[2].parse::<u64>() {
             return Ok((
@@ -1815,6 +1819,41 @@ mod tests {
         );
     }
 
+    #[test]
+    fn convert_arg_to_comparable_value_and_suffix_test() {
+        // Valid sign forms, matching GNU find's -size grammar.
+        assert_eq!(
+            convert_arg_to_comparable_value_and_suffix("-size", "5c").unwrap(),
+            (ComparableValue::EqualTo(5), "c".to_string()),
+        );
+        assert_eq!(
+            convert_arg_to_comparable_value_and_suffix("-size", "+5c").unwrap(),
+            (ComparableValue::MoreThan(5), "c".to_string()),
+        );
+        assert_eq!(
+            convert_arg_to_comparable_value_and_suffix("-size", "-5c").unwrap(),
+            (ComparableValue::LessThan(5), "c".to_string()),
+        );
+        // GNU accepts one extra '+' after the comparison sign.
+        assert_eq!(
+            convert_arg_to_comparable_value_and_suffix("-size", "++5c").unwrap(),
+            (ComparableValue::MoreThan(5), "c".to_string()),
+        );
+        assert_eq!(
+            convert_arg_to_comparable_value_and_suffix("-size", "-+5c").unwrap(),
+            (ComparableValue::LessThan(5), "c".to_string()),
+        );
+
+        // A non-numeric prefix ("x5c" used to be silently parsed as "5c") and the
+        // invalid double-sign forms are rejected, matching GNU.
+        for bad in ["x5c", "abc5c", "+-5c", "--5c", "+++5c"] {
+            assert!(
+                convert_arg_to_comparable_value_and_suffix("-size", bad).is_err(),
+                "expected `{bad}` to be rejected",
+            );
+        }
+    }
+
     #[test]
     fn convert_exception_arg_to_comparable_value_test() {
         let exception_args = ["1%2", "1%2%3", "1a2", "1%2a", "abc", "-", "+", "%"];