diff --git a/src/Interpreter/instructions.cpp b/src/Interpreter/instructions.cpp
index 04aea160..2eba848d 100644
--- a/src/Interpreter/instructions.cpp
+++ b/src/Interpreter/instructions.cpp
@@ -1268,6 +1268,31 @@ bool i_instr_conversion(Module *m, uint8_t opcode) {
     return true;
 }
 
+bool i_instr_extension(Module *m, uint8_t opcode) {
+    auto &v = m->stack[m->sp].value;
+
+    switch (opcode) {
+        case 0xc0:  // i32.extend8_s
+            v.int32 = static_cast<int8_t>(v.int32);
+            break;
+        case 0xc1:  // i32.extend16_s
+            v.int32 = static_cast<int16_t>(v.int32);
+            break;
+        case 0xc2:  // i64.extend8_s
+            v.int64 = static_cast<int8_t>(v.int64);
+            break;
+        case 0xc3:  // i64.extend16_s
+            v.int64 = static_cast<int16_t>(v.int64);
+            break;
+        case 0xc4:  // i64.extend32_s
+            v.int64 = static_cast<int32_t>(v.int64);
+            break;
+        default:
+            return false;
+    }
+    return true;
+}
+
 /**
  * 0xe0 ... 0xe3 callback operations
  */
diff --git a/src/Interpreter/instructions.h b/src/Interpreter/instructions.h
index 54a80f1b..f58f2cd4 100644
--- a/src/Interpreter/instructions.h
+++ b/src/Interpreter/instructions.h
@@ -72,4 +72,6 @@ bool i_instr_binary_f64(Module *m, uint8_t opcode);
 
 bool i_instr_conversion(Module *m, uint8_t opcode);
 
+bool i_instr_extension(Module *m, uint8_t opcode);
+
 bool i_instr_callback(Module *m, uint8_t opcode);
diff --git a/src/Interpreter/interpreter.cpp b/src/Interpreter/interpreter.cpp
index 9f22c6ac..834c4f4f 100644
--- a/src/Interpreter/interpreter.cpp
+++ b/src/Interpreter/interpreter.cpp
@@ -436,6 +436,11 @@ bool Interpreter::interpret(Module *m, bool waiting) {
                 success &= i_instr_conversion(m, opcode);
                 continue;
 
+                // extension operations
+            case 0xc0 ... 0xc4:
+                success &= i_instr_extension(m, opcode);
+                continue;
+
                 // callback operations
             case 0xe0 ... 0xe3:
                 success &= i_instr_callback(m, opcode);
diff --git a/tests/latch/core/i32_0.asserts.wast b/tests/latch/core/i32_0.asserts.wast
index 86378302..3b98ccb7 100644
--- a/tests/latch/core/i32_0.asserts.wast
+++ b/tests/latch/core/i32_0.asserts.wast
@@ -198,9 +198,13 @@
        (assert_return (invoke "popcnt" (i32.const 0xDEADBEEF)) (i32.const 24))
        (assert_return (invoke "extend8_s" (i32.const 0)) (i32.const 0))
        (assert_return (invoke "extend8_s" (i32.const 0x7f)) (i32.const 127))
+       (assert_return (invoke "extend8_s" (i32.const 0x80)) (i32.const -128))
+       (assert_return (invoke "extend8_s" (i32.const 0xff)) (i32.const -1))
        (assert_return (invoke "extend8_s" (i32.const -1)) (i32.const -1))
        (assert_return (invoke "extend16_s" (i32.const 0)) (i32.const 0))
        (assert_return (invoke "extend16_s" (i32.const 0x7fff)) (i32.const 32767))
+       (assert_return (invoke "extend16_s" (i32.const 0x8000)) (i32.const -32768))
+       (assert_return (invoke "extend16_s" (i32.const 0xffff)) (i32.const -1))
        (assert_return (invoke "extend16_s" (i32.const -1)) (i32.const -1))
        (assert_return (invoke "eqz" (i32.const 0)) (i32.const 1))
        (assert_return (invoke "eqz" (i32.const 1)) (i32.const 0))
diff --git a/tests/latch/core/i64_0.asserts.wast b/tests/latch/core/i64_0.asserts.wast
index bad63ead..6aef3586 100644
--- a/tests/latch/core/i64_0.asserts.wast
+++ b/tests/latch/core/i64_0.asserts.wast
@@ -131,9 +131,13 @@
        (assert_return (invoke "popcnt" (i64.const 0x00008000)) (i64.const 1))
        (assert_return (invoke "extend8_s" (i64.const 0)) (i64.const 0))
        (assert_return (invoke "extend8_s" (i64.const 0x7f)) (i64.const 127))
+       (assert_return (invoke "extend8_s" (i64.const 0x80)) (i64.const -128))
+       (assert_return (invoke "extend8_s" (i64.const 0xff)) (i64.const -1))
        (assert_return (invoke "extend8_s" (i64.const -1)) (i64.const -1))
        (assert_return (invoke "extend16_s" (i64.const 0)) (i64.const 0))
        (assert_return (invoke "extend16_s" (i64.const 0x7fff)) (i64.const 32767))
+       (assert_return (invoke "extend16_s" (i64.const 0x8000)) (i64.const -32768))
+       (assert_return (invoke "extend16_s" (i64.const 0xffff)) (i64.const -1))
        (assert_return (invoke "extend16_s" (i64.const -1)) (i64.const -1))
        (assert_return (invoke "extend32_s" (i64.const 0)) (i64.const 0))
        (assert_return (invoke "extend32_s" (i64.const 0x7fff)) (i64.const 32767))