diff --git a/include/chibi/sexp.h b/include/chibi/sexp.h
index 57722e57..3a2c75cb 100644
--- a/include/chibi/sexp.h
+++ b/include/chibi/sexp.h
@@ -1051,9 +1051,9 @@ SEXP_API void sexp_maybe_unblock_port (sexp ctx, sexp in);
   if (sexp_maybe_block_port(ctx, in, forcep))           \
     return sexp_global(ctx, SEXP_G_IO_BLOCK_ERROR)
 #else
-#define sexp_maybe_block_port(ctx, in, forcep) 0
-#define sexp_maybe_unblock_port(ctx, in) 0
-#define sexp_check_block_port(ctx, in, forcep) 0
+#define sexp_maybe_block_port(ctx, in, forcep)
+#define sexp_maybe_unblock_port(ctx, in)
+#define sexp_check_block_port(ctx, in, forcep)
 #endif
 
 #define SEXP_PORT_UNKNOWN_FLAGS -1uL
diff --git a/main.c b/main.c
index ee6d044c..073c64cc 100644
--- a/main.c
+++ b/main.c
@@ -86,9 +86,9 @@ static sexp check_exception (sexp ctx, sexp res) {
 }
 
 static sexp sexp_load_standard_repl_env (sexp ctx, sexp env, sexp k) {
-  sexp p, res = sexp_load_standard_env(ctx, env, k);
+  sexp res = sexp_load_standard_env(ctx, env, k);
 #if SEXP_USE_GREEN_THREADS
-  p  = sexp_param_ref(ctx, env, sexp_global(ctx, SEXP_G_CUR_IN_SYMBOL));
+  sexp p  = sexp_param_ref(ctx, env, sexp_global(ctx, SEXP_G_CUR_IN_SYMBOL));
   if (sexp_portp(p)) fcntl(sexp_port_fileno(p), F_SETFL, O_NONBLOCK);
   p  = sexp_param_ref(ctx, env, sexp_global(ctx, SEXP_G_CUR_OUT_SYMBOL));
   if (sexp_portp(p)) fcntl(sexp_port_fileno(p), F_SETFL, O_NONBLOCK);
diff --git a/vm.c b/vm.c
index b06ff59d..2a0c6f93 100644
--- a/vm.c
+++ b/vm.c
@@ -211,13 +211,13 @@ static void generate_opcode_app (sexp ctx, sexp app) {
       if (sexp_opcode_inverse(op)) {
         inv_default = 1;
       } else {
-        if (sexp_opcode_opt_param_p(op)) {
+        if (sexp_opcode_opt_param_p(op) && sexp_opcodep(sexp_opcode_data(op))) {
 #if SEXP_USE_GREEN_THREADS
           emit(ctx, SEXP_OP_PARAMETER_REF);
           emit_word(ctx, (sexp_uint_t)sexp_opcode_data(op));
           bytecode_preserve(ctx, sexp_opcode_data(op));
 #else
-          emit_push(ctx, sexp_opcode_data(op));
+          emit_push(ctx, sexp_opcode_data(sexp_opcode_data(op)));
 #endif
           emit(ctx, SEXP_OP_CDR);
         } else {
@@ -561,7 +561,7 @@ static int sexp_check_type(sexp ctx, sexp a, sexp b) {
   }
 #else
 #define sexp_fcall_return(x, i)                                 \
-  top -= i; _ARG1 = x; ip += s; sexp_check_exception(x);
+  top -= i; _ARG1 = x; ip += sizeof(sexp); sexp_check_exception();
 #endif
 
 #if SEXP_USE_DEBUG_VM