diff --git a/src/mnemonic.c b/src/mnemonic.c
index 06f5f908a..510277faa 100644
--- a/src/mnemonic.c
+++ b/src/mnemonic.c
@@ -59,8 +59,9 @@ char *mnemonic_from_bytes(const struct words *w, const unsigned char *bytes, siz
     return str;
 }
 
-int mnemonic_to_bytes(const struct words *w, const char *mnemonic,
-                      unsigned char *bytes_out, size_t len, size_t *written)
+int mnemonic_to_bytes_internal(const struct words *w, const char *mnemonic,
+                               size_t(*lookup_fn)(const struct words *, const char *),
+                               unsigned char *bytes_out, size_t len, size_t *written)
 {
     struct words *mnemonic_w = wordlist_init(mnemonic);
     size_t i;
@@ -80,7 +81,7 @@ int mnemonic_to_bytes(const struct words *w, const char *mnemonic,
     wally_clear(bytes_out, len);
 
     for (i = 0; i < mnemonic_w->len; ++i) {
-        size_t idx = wordlist_lookup_word(w, mnemonic_w->indices[i]);
+        size_t idx = lookup_fn(w, mnemonic_w->indices[i]);
         if (!idx) {
             wordlist_free(mnemonic_w);
             wally_clear(bytes_out, len);
@@ -95,3 +96,13 @@ int mnemonic_to_bytes(const struct words *w, const char *mnemonic,
     wordlist_free(mnemonic_w);
     return WALLY_OK;
 }
+
+int mnemonic_to_bytes(const struct words *w, const char *mnemonic,
+                      unsigned char *bytes_out, size_t len, size_t *written) {
+    return mnemonic_to_bytes_internal(w, mnemonic, wordlist_lookup_word, bytes_out, len, written);
+}
+
+int mnemonic_prefix_to_bytes(const struct words *w, const char *mnemonic,
+                             unsigned char *bytes_out, size_t len, size_t *written) {
+    return mnemonic_to_bytes_internal(w, mnemonic, wordlist_lookup_prefix, bytes_out, len, written);
+}
diff --git a/src/mnemonic.h b/src/mnemonic.h
index a17797680..e6060b526 100644
--- a/src/mnemonic.h
+++ b/src/mnemonic.h
@@ -33,4 +33,20 @@ int mnemonic_to_bytes(
     size_t len,
     size_t *written);
 
+/**
+ * Convert a mnemonic representation into a block of bytes. Accepts unique prefixes of wordlist words.
+ *
+ * @w: List of words.
+ * @mnemonic: Mnemonic sentence to store.
+ * @bytes_out: Where to store the converted representation.
+ * @len: The length of @bytes_out in bytes.
+ * @written: Destination for the number of bytes written.
+ */
+int mnemonic_prefix_to_bytes(
+    const struct words *w,
+    const char *mnemonic,
+    unsigned char *bytes_out,
+    size_t len,
+    size_t *written);
+
 #endif /* LIBWALLY_MNEMONIC_H */
diff --git a/src/wordlist.c b/src/wordlist.c
index fb1481931..98bac021d 100644
--- a/src/wordlist.c
+++ b/src/wordlist.c
@@ -83,6 +83,24 @@ size_t wordlist_lookup_word(const struct words *w, const char *word)
     return found ? found - w->indices + 1u : 0u;
 }
 
+size_t wordlist_lookup_prefix(const struct words *w, const char *prefix)
+{
+    const size_t prefix_len = strlen(prefix);
+    size_t found = 0;
+
+    size_t i;
+    for (i = 0; i < w->len; ++i) {
+        if (!strncmp(prefix, w->indices[i], prefix_len)) {
+            if (found) {
+                return 0;  // prefix match is not unique
+            }
+            found = i + 1;
+        }
+    }
+
+    return found;
+}
+
 const char *wordlist_lookup_index(const struct words *w, size_t idx)
 {
     if (idx >= w->len)
diff --git a/src/wordlist.h b/src/wordlist.h
index c8189672e..64f758d9b 100644
--- a/src/wordlist.h
+++ b/src/wordlist.h
@@ -45,6 +45,19 @@ size_t wordlist_lookup_word(
     const struct words *w,
     const char *word);
 
+/**
+ * Find the unique word matching a given prefix in a wordlist.
+ *
+ * @w: Parsed list of words to look up in.
+ * @word: The prefix to look up.
+ *
+ * Returns 0 if not found OR not unique, idx + 1 otherwise.
+ * @see wordlist_init.
+ */
+size_t wordlist_lookup_prefix(
+    const struct words *w,
+    const char *prefix);
+
 /**
  * Return the Nth word in a wordlist.
  *