diff --git a/src/core/CallExtern.go b/src/core/CallExtern.go
index 8d3f358..abb1a7a 100644
--- a/src/core/CallExtern.go
+++ b/src/core/CallExtern.go
@@ -2,7 +2,10 @@ package core
 
 import (
 	"fmt"
+	"slices"
 
+	"git.akyoto.dev/cli/q/src/asm"
+	"git.akyoto.dev/cli/q/src/cpu"
 	"git.akyoto.dev/cli/q/src/expression"
 	"git.akyoto.dev/cli/q/src/types"
 	"git.akyoto.dev/cli/q/src/x86"
@@ -11,6 +14,17 @@ import (
 // CallExtern calls an external function.
 func (f *Function) CallExtern(fn *Function, parameters []*expression.Expression) ([]types.Type, error) {
 	f.DLLs = f.DLLs.Append(fn.Package, fn.Name)
+
+	var pushedRegisters []cpu.Register
+
+	for _, register := range x86.WindowsVolatileRegisters {
+		if f.RegisterIsUsed(register) {
+			f.Register(asm.PUSH, register)
+			f.FreeRegister(register)
+			pushedRegisters = append(pushedRegisters, register)
+		}
+	}
+
 	registers := x86.WindowsInputRegisters[:len(parameters)]
 	err := f.BeforeCall(fn, parameters, registers)
 
@@ -19,5 +33,14 @@ func (f *Function) CallExtern(fn *Function, parameters []*expression.Expression)
 	}
 
 	f.DLLCall(fmt.Sprintf("%s.%s", fn.Package, fn.Name))
+
+	for _, register := range registers {
+		f.FreeRegister(register)
+	}
+
+	for _, register := range slices.Backward(pushedRegisters) {
+		f.Register(asm.POP, register)
+	}
+
 	return fn.OutputTypes, nil
 }
diff --git a/src/x86/Registers.go b/src/x86/Registers.go
index 0ed7c5f..090a678 100644
--- a/src/x86/Registers.go
+++ b/src/x86/Registers.go
@@ -22,12 +22,13 @@ const (
 )
 
 var (
-	AllRegisters           = []cpu.Register{RAX, RCX, RDX, RBX, RSP, RBP, RSI, RDI, R8, R9, R10, R11, R12, R13, R14, R15}
-	SyscallInputRegisters  = []cpu.Register{RAX, RDI, RSI, RDX, R10, R8, R9}
-	SyscallOutputRegisters = []cpu.Register{RAX, RCX, R11}
-	GeneralRegisters       = []cpu.Register{RCX, RBX, R11, R12, R13, R14, R15, RBP}
-	InputRegisters         = SyscallInputRegisters
-	OutputRegisters        = SyscallInputRegisters
-	WindowsInputRegisters  = []cpu.Register{RCX, RDX, R8, R9}
-	WindowsOutputRegisters = []cpu.Register{RAX}
+	AllRegisters             = []cpu.Register{RAX, RCX, RDX, RBX, RSP, RBP, RSI, RDI, R8, R9, R10, R11, R12, R13, R14, R15}
+	SyscallInputRegisters    = []cpu.Register{RAX, RDI, RSI, RDX, R10, R8, R9}
+	SyscallOutputRegisters   = []cpu.Register{RAX, RCX, R11}
+	GeneralRegisters         = []cpu.Register{RBX, R12, R13, R14, R15, RCX, R11, RBP}
+	InputRegisters           = SyscallInputRegisters
+	OutputRegisters          = SyscallInputRegisters
+	WindowsInputRegisters    = []cpu.Register{RCX, RDX, R8, R9}
+	WindowsOutputRegisters   = []cpu.Register{RAX}
+	WindowsVolatileRegisters = []cpu.Register{RCX, RDX, R8, R9, R10, R11}
 )