diff --git a/src/libcoreint/interpreter.c b/src/libcoreint/interpreter.c
index d3bc21132..a9a4d5e74 100644
--- a/src/libcoreint/interpreter.c
+++ b/src/libcoreint/interpreter.c
@@ -46,7 +46,7 @@ run_int (void)
 {
   JERRY_ASSERT( __program != NULL );
 
-  const int start_pos = 0;
+  const interp_bytecode_idx start_pos = 0;
   ecma_object_t *this_binding_p = NULL;
   ecma_object_t *lex_env_p = ecma_create_lexical_environment (NULL,
                                                               ECMA_LEXICAL_ENVIRONMENT_DECLARATIVE);
@@ -88,7 +88,7 @@ run_int (void)
 }
 
 ecma_completion_value_t
-run_int_from_pos (int start_pos,
+run_int_from_pos (interp_bytecode_idx start_pos,
                   ecma_object_t *this_binding_p,
                   ecma_object_t *lex_env_p,
                   bool is_strict)
@@ -111,7 +111,7 @@ run_int_from_pos (int start_pos,
   JERRY_ASSERT( ecma_is_value_empty( regs[0]) );
 
   struct __int_data int_data;
-  int_data.pos = start_pos + 1;
+  int_data.pos = (interp_bytecode_idx) (start_pos + 1);
   int_data.this_binding_p = this_binding_p;
   int_data.lex_env_p = lex_env_p;
   int_data.is_strict = is_strict;
diff --git a/src/libcoreint/interpreter.h b/src/libcoreint/interpreter.h
index 253b77565..d82473b10 100644
--- a/src/libcoreint/interpreter.h
+++ b/src/libcoreint/interpreter.h
@@ -20,9 +20,11 @@
 #include "globals.h"
 #include "opcodes.h"
 
+typedef uint16_t interp_bytecode_idx;
+
 struct __int_data
 {
-  int pos; /**< current opcode to execute */
+  interp_bytecode_idx pos; /**< current opcode to execute */
   ecma_object_t *this_binding_p; /**< this binding for current context */
   ecma_object_t *lex_env_p; /**< current lexical environment */
   bool is_strict; /**< is current code execution mode strict? */
@@ -33,7 +35,7 @@ struct __int_data
 
 void init_int (const OPCODE* program_p);
 bool run_int (void);
-ecma_completion_value_t run_int_from_pos (int start_pos,
+ecma_completion_value_t run_int_from_pos (interp_bytecode_idx start_pos,
                                           ecma_object_t *this_binding_p,
                                           ecma_object_t *lex_env_p,
                                           bool is_strict);
diff --git a/src/libcoreint/opcodes.c b/src/libcoreint/opcodes.c
index e9161574f..2f67101c8 100644
--- a/src/libcoreint/opcodes.c
+++ b/src/libcoreint/opcodes.c
@@ -564,7 +564,9 @@ ecma_completion_value_t
 opfunc_jmp_down (OPCODE opdata, /**< operation data */
                  struct __int_data *int_data) /**< interpreter context */
 {
-  int_data->pos += opdata.data.jmp_down.opcode_count;
+  JERRY_ASSERT( int_data->pos <= int_data->pos + opdata.data.jmp_up.opcode_count );
+
+  int_data->pos = (interp_bytecode_idx) ( int_data->pos + opdata.data.jmp_down.opcode_count );
 
   return ecma_make_empty_completion_value();
 } /* opfunc_jmp_down */
@@ -579,9 +581,9 @@ ecma_completion_value_t
 opfunc_jmp_up (OPCODE opdata, /**< operation data */
                struct __int_data *int_data) /**< interpreter context */
 {
-  int_data->pos -= opdata.data.jmp_up.opcode_count;
+  JERRY_ASSERT( int_data->pos >= opdata.data.jmp_up.opcode_count );
 
-  JERRY_ASSERT( int_data->pos >= 0 );
+  int_data->pos = (interp_bytecode_idx) ( int_data->pos - opdata.data.jmp_down.opcode_count );
 
   return ecma_make_empty_completion_value();
 } /* opfunc_jmp_up */