diff --git a/src/operator/attribute.rs b/src/operator/attribute.rs
index 73e9c66..87ef7cb 100644
--- a/src/operator/attribute.rs
+++ b/src/operator/attribute.rs
@@ -197,9 +197,9 @@ impl FromOpAttr for String {
 	where
 		Self: Sized
 	{
-		let mut out = vec![0_u8; len];
-		ortsys![unsafe ReadOpAttr(attr, ort_sys::OrtOpAttrType::ORT_OP_ATTR_STRING, out.as_mut_ptr().cast(), len, &mut len)?];
-		debug_assert_eq!(out.len(), len, "int attribute is smaller/larger than expected");
+		let mut out = vec![0_u8; len + 1];
+		ortsys![unsafe ReadOpAttr(attr, ort_sys::OrtOpAttrType::ORT_OP_ATTR_STRING, out.as_mut_ptr().cast(), len + 1, &mut len)?];
+		debug_assert_eq!(out.len(), len + 1, "string attribute is smaller/larger than expected");
 		CString::from_vec_with_nul(out)
 			.map_err(|_| Error::new("invalid string attribute contents"))
 			.and_then(|f| f.into_string().map_err(|_| Error::new("invalid string attribute contents")))