diff --git a/fuzz/fuzz_targets/roundtrip_concrete.rs b/fuzz/fuzz_targets/roundtrip_concrete.rs
index fdaf62f21..6a30ef797 100644
--- a/fuzz/fuzz_targets/roundtrip_concrete.rs
+++ b/fuzz/fuzz_targets/roundtrip_concrete.rs
@@ -1,6 +1,8 @@
 
 extern crate miniscript;
 
+#[path = "../src/util.rs"] mod util;
+
 use std::str::FromStr;
 use miniscript::{policy, DummyKey};
 
@@ -36,22 +38,7 @@ fn main() {
 
 #[cfg(test)]
 mod tests {
-    fn extend_vec_from_hex(hex: &str, out: &mut Vec<u8>) {
-        let mut b = 0;
-        for (idx, c) in hex.as_bytes().iter().enumerate() {
-            b <<= 4;
-            match *c {
-                b'A'...b'F' => b |= c - b'A' + 10,
-                b'a'...b'f' => b |= c - b'a' + 10,
-                b'0'...b'9' => b |= c - b'0',
-                _ => panic!("Bad hex"),
-            }
-            if (idx & 1) == 1 {
-                out.push(b);
-                b = 0;
-            }
-        }
-    }
+    use util::extend_vec_from_hex;
 
     #[test]
     fn duplicate_crash() {
diff --git a/fuzz/fuzz_targets/roundtrip_descriptor.rs b/fuzz/fuzz_targets/roundtrip_descriptor.rs
index ac1b2bcdb..f540d239d 100644
--- a/fuzz/fuzz_targets/roundtrip_descriptor.rs
+++ b/fuzz/fuzz_targets/roundtrip_descriptor.rs
@@ -1,8 +1,9 @@
 
 extern crate miniscript;
 
-use miniscript::{Descriptor, DummyKey};
+#[path = "../src/util.rs"] mod util;
 
+use miniscript::{Descriptor, DummyKey};
 use std::str::FromStr;
 
 fn do_test(data: &[u8]) {
@@ -36,22 +37,7 @@ fn main() {
 
 #[cfg(test)]
 mod tests {
-    fn extend_vec_from_hex(hex: &str, out: &mut Vec<u8>) {
-        let mut b = 0;
-        for (idx, c) in hex.as_bytes().iter().enumerate() {
-            b <<= 4;
-            match *c {
-                b'A'...b'F' => b |= c - b'A' + 10,
-                b'a'...b'f' => b |= c - b'a' + 10,
-                b'0'...b'9' => b |= c - b'0',
-                _ => panic!("Bad hex"),
-            }
-            if (idx & 1) == 1 {
-                out.push(b);
-                b = 0;
-            }
-        }
-    }
+    use util::extend_vec_from_hex;
 
     #[test]
     fn duplicate_crash() {
diff --git a/fuzz/fuzz_targets/roundtrip_miniscript_script.rs b/fuzz/fuzz_targets/roundtrip_miniscript_script.rs
index 3ce8ad939..7f1d713f9 100644
--- a/fuzz/fuzz_targets/roundtrip_miniscript_script.rs
+++ b/fuzz/fuzz_targets/roundtrip_miniscript_script.rs
@@ -1,6 +1,8 @@
 
 extern crate miniscript;
 
+#[path = "../src/util.rs"] mod util;
+
 use miniscript::Miniscript;
 use miniscript::bitcoin::blockdata::script;
 
@@ -37,22 +39,7 @@ fn main() {
 
 #[cfg(test)]
 mod tests {
-    fn extend_vec_from_hex(hex: &str, out: &mut Vec<u8>) {
-        let mut b = 0;
-        for (idx, c) in hex.as_bytes().iter().enumerate() {
-            b <<= 4;
-            match *c {
-                b'A'...b'F' => b |= c - b'A' + 10,
-                b'a'...b'f' => b |= c - b'a' + 10,
-                b'0'...b'9' => b |= c - b'0',
-                _ => panic!("Bad hex"),
-            }
-            if (idx & 1) == 1 {
-                out.push(b);
-                b = 0;
-            }
-        }
-    }
+    use util::extend_vec_from_hex;
 
     #[test]
     fn duplicate_crash() {
diff --git a/fuzz/fuzz_targets/roundtrip_miniscript_str.rs b/fuzz/fuzz_targets/roundtrip_miniscript_str.rs
index 3cf46712b..d0f5bd4b5 100644
--- a/fuzz/fuzz_targets/roundtrip_miniscript_str.rs
+++ b/fuzz/fuzz_targets/roundtrip_miniscript_str.rs
@@ -1,8 +1,9 @@
 
 extern crate miniscript;
 
-use std::str::FromStr;
+#[path = "../src/util.rs"] mod util;
 
+use std::str::FromStr;
 use miniscript::{DummyKey};
 use miniscript::Miniscript;
 
@@ -36,22 +37,7 @@ fn main() {
 
 #[cfg(test)]
 mod tests {
-    fn extend_vec_from_hex(hex: &str, out: &mut Vec<u8>) {
-        let mut b = 0;
-        for (idx, c) in hex.as_bytes().iter().enumerate() {
-            b <<= 4;
-            match *c {
-                b'A'...b'F' => b |= c - b'A' + 10,
-                b'a'...b'f' => b |= c - b'a' + 10,
-                b'0'...b'9' => b |= c - b'0',
-                _ => panic!("Bad hex"),
-            }
-            if (idx & 1) == 1 {
-                out.push(b);
-                b = 0;
-            }
-        }
-    }
+    use util::extend_vec_from_hex;
 
     #[test]
     fn duplicate_crash() {
diff --git a/fuzz/fuzz_targets/roundtrip_policy.rs b/fuzz/fuzz_targets/roundtrip_policy.rs
index ab93e29cf..27d49913b 100644
--- a/fuzz/fuzz_targets/roundtrip_policy.rs
+++ b/fuzz/fuzz_targets/roundtrip_policy.rs
@@ -1,6 +1,8 @@
 
 extern crate miniscript;
 
+#[path = "../src/util.rs"] mod util;
+
 use std::str::FromStr;
 use miniscript::{policy, DummyKey};
 
@@ -41,22 +43,7 @@ fn main() {
 
 #[cfg(test)]
 mod tests {
-    fn extend_vec_from_hex(hex: &str, out: &mut Vec<u8>) {
-        let mut b = 0;
-        for (idx, c) in hex.as_bytes().iter().enumerate() {
-            b <<= 4;
-            match *c {
-                b'A'...b'F' => b |= c - b'A' + 10,
-                b'a'...b'f' => b |= c - b'a' + 10,
-                b'0'...b'9' => b |= c - b'0',
-                _ => panic!("Bad hex"),
-            }
-            if (idx & 1) == 1 {
-                out.push(b);
-                b = 0;
-            }
-        }
-    }
+    use util::extend_vec_from_hex;
 
     #[test]
     fn duplicate_crash() {
@@ -64,11 +51,4 @@ mod tests {
         extend_vec_from_hex("00", &mut a);
         super::do_test(&a);
     }
-
-    #[test]
-    fn duplicate_crash_2() {
-        let mut a = Vec::new();
-        extend_vec_from_hex("746872657368", &mut a); // thresh
-        super::do_test(&a);
-    }
 }
diff --git a/fuzz/fuzz_targets/roundtrip_semantic.rs b/fuzz/fuzz_targets/roundtrip_semantic.rs
index e65e95a48..a78c2fc09 100644
--- a/fuzz/fuzz_targets/roundtrip_semantic.rs
+++ b/fuzz/fuzz_targets/roundtrip_semantic.rs
@@ -1,6 +1,8 @@
 
 extern crate miniscript;
 
+#[path = "../src/util.rs"] mod util;
+
 use std::str::FromStr;
 use miniscript::{policy, DummyKey};
 
@@ -36,27 +38,12 @@ fn main() {
 
 #[cfg(test)]
 mod tests {
-    fn extend_vec_from_hex(hex: &str, out: &mut Vec<u8>) {
-        let mut b = 0;
-        for (idx, c) in hex.as_bytes().iter().enumerate() {
-            b <<= 4;
-            match *c {
-                b'A'...b'F' => b |= c - b'A' + 10,
-                b'a'...b'f' => b |= c - b'a' + 10,
-                b'0'...b'9' => b |= c - b'0',
-                _ => panic!("Bad hex"),
-            }
-            if (idx & 1) == 1 {
-                out.push(b);
-                b = 0;
-            }
-        }
-    }
-
+    use util::extend_vec_from_hex;
+    
     #[test]
     fn duplicate_crash() {
         let mut a = Vec::new();
         extend_vec_from_hex("048531e80700ae6400670000af5168", &mut a);
         super::do_test(&a);
     }
-}
+}
\ No newline at end of file
diff --git a/fuzz/src/util.rs b/fuzz/src/util.rs
new file mode 100644
index 000000000..8d2ba7305
--- /dev/null
+++ b/fuzz/src/util.rs
@@ -0,0 +1,17 @@
+#[cfg(test)]
+pub fn extend_vec_from_hex(hex: &str, out: &mut Vec<u8>) {
+    let mut b = 0;
+    for (idx, c) in hex.as_bytes().iter().enumerate() {
+        b <<= 4;
+        match *c {
+            b'A'...b'F' => b |= c - b'A' + 10,
+            b'a'...b'f' => b |= c - b'a' + 10,
+            b'0'...b'9' => b |= c - b'0',
+            _ => panic!("Bad hex"),
+        }
+        if (idx & 1) == 1 {
+            out.push(b);
+            b = 0;
+        }
+    }
+}
diff --git a/src/policy/semantic.rs b/src/policy/semantic.rs
index e1705bc6f..f0a6b8d62 100644
--- a/src/policy/semantic.rs
+++ b/src/policy/semantic.rs
@@ -485,6 +485,11 @@ mod tests {
              )"
         )
         .is_ok());
+
+        assert_eq!(
+            StringPolicy::from_str("thresh").unwrap_err().to_string(),
+            "unexpected «thresh without args»"
+        );
     }
 
     #[test]