diff --git a/src/main/wacc/backend/Stack.scala b/src/main/wacc/backend/Stack.scala
index 0949ecb..94b329a 100644
--- a/src/main/wacc/backend/Stack.scala
+++ b/src/main/wacc/backend/Stack.scala
@@ -50,7 +50,7 @@ class Stack {
     * @param sizes
     *   The sizes of the values to reserve space for.
     */
-  def reserve(sizes: List[Size]): AsmLine = {
+  def reserve(sizes: Size*): AsmLine = {
     sizes.foreach { itemSize =>
       stack += stack.size -> StackValue(itemSize, sizeBytes)
     }
diff --git a/src/main/wacc/backend/asmGenerator.scala b/src/main/wacc/backend/asmGenerator.scala
index 8dc67f6..60e0b47 100644
--- a/src/main/wacc/backend/asmGenerator.scala
+++ b/src/main/wacc/backend/asmGenerator.scala
@@ -93,7 +93,9 @@ object asmGenerator {
     )
   }
 
-  private def wrapBuiltinFunc(labelName: String, funcBody: Chain[AsmLine]): Chain[AsmLine] = {
+  private def wrapBuiltinFunc(labelName: String, funcBody: Chain[AsmLine])(using
+      stack: Stack
+  ): Chain[AsmLine] = {
     var chain = Chain.one[AsmLine](LabelDef(labelName))
     chain ++= funcPrologue()
     chain ++= funcBody
@@ -108,6 +110,7 @@ object asmGenerator {
     given stack: Stack = Stack()
     // Setup the stack with param 7 and up
     func.params.drop(argRegs.size).foreach(stack.reserve(_))
+    stack.reserve(Q64) // Reserve return pointer slot
     var chain = Chain.one[AsmLine](LabelDef(labelGenerator.getLabel(func.name)))
     chain ++= funcPrologue()
     // Push the rest of params onto the stack for simplicity
@@ -120,6 +123,7 @@ object asmGenerator {
   }
 
   private def generateBuiltInFuncs()(using
+      stack: Stack,
       labelGenerator: LabelGenerator
   ): Chain[AsmLine] = {
     var chain = Chain.empty[AsmLine]
@@ -425,9 +429,9 @@ object asmGenerator {
     chain
   }
 
-  private def funcPrologue(): Chain[AsmLine] = {
+  private def funcPrologue()(using stack: Stack): Chain[AsmLine] = {
     var chain = Chain.empty[AsmLine]
-    chain += Push(RBP)
+    chain += stack.push(Q64, RBP)
     chain += Move(RBP, Register(Q64, SP))
     chain
   }
diff --git a/src/test/wacc/examples.scala b/src/test/wacc/examples.scala
index 988a6d0..01e4c30 100644
--- a/src/test/wacc/examples.scala
+++ b/src/test/wacc/examples.scala
@@ -90,8 +90,8 @@ class ParallelExamplesSpec extends AnyFlatSpec with BeforeAndAfterAll {
       // "^.*wacc-examples/valid/basic/exit.*$",
       // "^.*wacc-examples/valid/basic/skip.*$",
       // "^.*wacc-examples/valid/expressions.*$",
-      "^.*wacc-examples/valid/function/nested_functions.*$",
-      "^.*wacc-examples/valid/function/simple_functions.*$",
+      // "^.*wacc-examples/valid/function/nested_functions.*$",
+      // "^.*wacc-examples/valid/function/simple_functions.*$",
       // "^.*wacc-examples/valid/if.*$",
       // "^.*wacc-examples/valid/IO/print.*$",
       // "^.*wacc-examples/valid/IO/read.*$",