diff --git a/eval.c b/eval.c
index 04b11688..1dd1e511 100644
--- a/eval.c
+++ b/eval.c
@@ -2202,7 +2202,7 @@ sexp sexp_make_null_env_op (sexp ctx, sexp self, sexp_sint_t n, sexp version) {
   return e;
 }
 
-struct sexp_opcode_struct* sexp_primitive_opcodes;  /* from opcodes.c */
+extern struct sexp_opcode_struct* sexp_primitive_opcodes;  /* from opcodes.c */
 
 sexp sexp_make_primitive_env_op (sexp ctx, sexp self, sexp_sint_t n, sexp version) {
   int i;