diff --git a/content/07a_opcodes/07_environment.ipynb b/content/07a_opcodes/07_environment.ipynb
index fc01072..fe3c673 100644
--- a/content/07a_opcodes/07_environment.ipynb
+++ b/content/07a_opcodes/07_environment.ipynb
@@ -69,7 +69,7 @@
    "outputs": [],
    "source": [
     "def balance(evm):\n",
-    "    address = cpu.stack.pop()\n",
+    "    address = evm.stack.pop()\n",
     "    evm.stack.push(99999999999)\n",
     "\n",
     "    evm.pc += 1\n",
@@ -249,7 +249,7 @@
    "outputs": [],
    "source": [
     "def calldatacopy(evm):\n",
-    "    destOffset = cpu.stack.pop()\n",
+    "    destOffset = evm.stack.pop()\n",
     "    offset = evm.stack.pop()\n",
     "    size = evm.stack.pop()\n",
     "\n",