diff --git a/rust/CHANGELOG.md b/rust/CHANGELOG.md
index f384b40a..f51e58ec 100644
--- a/rust/CHANGELOG.md
+++ b/rust/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Changelog
 
+# Unreleased
+
+- fix(rust): Interpret `max_depth` in proof specs as 128 if left to 0 [#371](https://github.com/cosmos/ics23/pull/371).
+
 # v0.12.0
 
 - chore(rust): Update `prost` to v0.13 ([#335](https://github.com/cosmos/ics23/pull/335), [#336](https://github.com/cosmos/ics23/pull/336))
diff --git a/rust/src/api.rs b/rust/src/api.rs
index 6ba17b6d..030c2c29 100644
--- a/rust/src/api.rs
+++ b/rust/src/api.rs
@@ -580,6 +580,69 @@ mod tests {
         verify_test_vector("../testdata/smt/nonexist_middle.json", &spec)
     }
 
+    #[derive(Deserialize)]
+    #[serde(rename_all = "PascalCase")]
+    struct ExistenceProofTest {
+        proof: crate::ExistenceProof,
+        is_err: bool,
+        expected: Option<Vec<u8>>,
+    }
+
+    #[test]
+    #[cfg(feature = "std")]
+    fn test_existence_proof() -> Result<()> {
+        use crate::calculate_existence_root;
+
+        let data = std::fs::read_to_string("../testdata/TestExistenceProofData.json")?;
+        let tests: BTreeMap<String, ExistenceProofTest> = serde_json::from_str(&data)?;
+
+        for (name, test) in tests {
+            println!("Test: {name}");
+            let result = calculate_existence_root::<HostFunctionsManager>(&test.proof);
+            if test.is_err {
+                assert!(result.is_err());
+            } else {
+                assert!(result.is_ok());
+                assert_eq!(
+                    result.unwrap().as_slice(),
+                    test.expected.unwrap().as_slice()
+                );
+            }
+        }
+
+        Ok(())
+    }
+
+    #[derive(Deserialize)]
+    #[serde(rename_all = "PascalCase")]
+    struct CheckAgainstSpecTest {
+        proof: crate::ExistenceProof,
+        spec: crate::ProofSpec,
+        err: String,
+    }
+
+    #[test]
+    #[cfg(feature = "std")]
+    fn test_check_against_spec() -> Result<()> {
+        use crate::verify::check_existence_spec;
+
+        let data = std::fs::read_to_string("../testdata/TestCheckAgainstSpecData.json")?;
+        let tests: BTreeMap<String, CheckAgainstSpecTest> = serde_json::from_str(&data)?;
+
+        for (name, test) in tests {
+            println!("Test: {name}");
+            let result = check_existence_spec(&test.proof, &test.spec);
+            if test.err.is_empty() {
+                assert!(result.is_ok());
+            } else {
+                assert!(result.is_err());
+                // assert_eq!(result.unwrap_err().to_string(), test.err);
+            }
+        }
+
+        Ok(())
+    }
+
     #[cfg(feature = "std")]
     fn load_batch(files: &[&str]) -> Result<(ics23::CommitmentProof, Vec<RefData>)> {
         let (data, entries) = files
diff --git a/rust/src/lib.rs b/rust/src/lib.rs
index 4799357b..aff96078 100644
--- a/rust/src/lib.rs
+++ b/rust/src/lib.rs
@@ -14,6 +14,10 @@ mod verify;
 mod ics23 {
     include!("cosmos.ics23.v1.rs");
 
+    impl ProofSpec {
+        pub const DEFAULT_MAX_DEPTH: i32 = 128;
+    }
+
     #[cfg(feature = "serde")]
     include!("cosmos.ics23.v1.serde.rs");
 }
diff --git a/rust/src/verify.rs b/rust/src/verify.rs
index ade0b93a..01eee6a2 100644
--- a/rust/src/verify.rs
+++ b/rust/src/verify.rs
@@ -114,31 +114,47 @@ fn calculate_existence_root_for_spec<H: HostFunctionsProvider>(
     }
 }
 
-fn check_existence_spec(proof: &ics23::ExistenceProof, spec: &ics23::ProofSpec) -> Result<()> {
-    if let (Some(leaf), Some(leaf_spec)) = (&proof.leaf, &spec.leaf_spec) {
-        ensure_leaf_prefix(&leaf.prefix, spec)?;
-        ensure_leaf(leaf, leaf_spec)?;
-        // ensure min/max depths
-        if spec.min_depth != 0 {
-            ensure!(
-                proof.path.len() >= spec.min_depth as usize,
-                "Too few InnerOps: {}",
-                proof.path.len(),
-            );
-            ensure!(
-                proof.path.len() <= spec.max_depth as usize,
-                "Too many InnerOps: {}",
-                proof.path.len(),
-            );
-        }
-        for (idx, step) in proof.path.iter().enumerate() {
-            ensure_inner_prefix(&step.prefix, spec, (idx as i64) + 1, step.hash)?;
-            ensure_inner(step, spec)?;
-        }
-        Ok(())
+pub(crate) fn check_existence_spec(
+    proof: &ics23::ExistenceProof,
+    spec: &ics23::ProofSpec,
+) -> Result<()> {
+    let Some(leaf) = &proof.leaf else {
+        bail!("existence Proof needs defined LeafOp");
+    };
+
+    let Some(leaf_spec) = &spec.leaf_spec else {
+        bail!("existence Proof needs defined LeafSpec");
+    };
+
+    ensure_leaf_prefix(&leaf.prefix, spec)?;
+    ensure_leaf(leaf, leaf_spec)?;
+
+    let max_depth = if spec.max_depth == 0 {
+        ics23::ProofSpec::DEFAULT_MAX_DEPTH
     } else {
-        bail!("Leaf and Leaf Spec must be set")
+        spec.max_depth
+    };
+
+    // ensure min/max depths
+    if spec.min_depth != 0 {
+        ensure!(
+            proof.path.len() >= spec.min_depth as usize,
+            "innerOps depth too short: {}",
+            proof.path.len(),
+        );
+        ensure!(
+            proof.path.len() <= max_depth as usize,
+            "innerOps depth too long: {}",
+            proof.path.len(),
+        );
+    }
+
+    for (idx, step) in proof.path.iter().enumerate() {
+        ensure_inner_prefix(&step.prefix, spec, (idx as i64) + 1, step.hash)?;
+        ensure_inner(step, spec)?;
     }
+
+    Ok(())
 }
 
 fn ensure_leaf(leaf: &ics23::LeafOp, leaf_spec: &ics23::LeafOp) -> Result<()> {