diff --git a/pyhmmer/easel.pxd b/pyhmmer/easel.pxd
index be4aee8..11fa885 100644
--- a/pyhmmer/easel.pxd
+++ b/pyhmmer/easel.pxd
@@ -43,13 +43,13 @@ cdef class GeneticCode:
     cdef readonly Alphabet     nucleotide_alphabet
     cdef          ESL_GENCODE* _gcode
 
-    cdef void _translate(
+    cdef int _translate(
         self,
         const ESL_DSQ* seq,
         int64_t seqlen,
         ESL_DSQ* out,
         int64_t outlen
-    ) except * nogil
+    ) except -1 nogil
 
     cpdef VectorU8 translate(self, const ESL_DSQ[::1] sequence)
 
diff --git a/pyhmmer/easel.pyx b/pyhmmer/easel.pyx
index 5e1c137..4f4259d 100644
--- a/pyhmmer/easel.pyx
+++ b/pyhmmer/easel.pyx
@@ -545,13 +545,13 @@ cdef class GeneticCode:
 
     # --- Utils --------------------------------------------------------------
 
-    cdef void _translate(
+    cdef int _translate(
         self,
         const ESL_DSQ* seq,
         int64_t seqlen,
         ESL_DSQ* out,
         int64_t outlen
-    ) except * nogil:
+    ) except -1 nogil:
         cdef int     aa
         cdef int64_t i
         cdef int64_t j
@@ -567,6 +567,8 @@ cdef class GeneticCode:
                 raise ValueError(f"Failed to translate codon at index {j!r}")
             out[i] = aa
 
+        return 0
+
     # --- Methods ------------------------------------------------------------
 
     cpdef VectorU8 translate(self, const ESL_DSQ[::1] sequence):