diff --git a/examples/prime/prime.q b/examples/prime/prime.q
index 7d639a2..f29c701 100644
--- a/examples/prime/prime.q
+++ b/examples/prime/prime.q
@@ -9,7 +9,7 @@ main() {
 			return
 		}
 
-		if isPrime(i) == 1 {
+		if isPrime(i) {
 			if i != 2 {
 				io.out(" ")
 			}
@@ -23,22 +23,22 @@ main() {
 
 isPrime(x int) -> bool {
 	if x == 2 {
-		return 1
+		return true
 	}
 
 	if x % 2 == 0 {
-		return 0
+		return false
 	}
 
 	i := 3
 
 	loop {
 		if i * i > x {
-			return 1
+			return true
 		}
 
 		if x % i == 0 {
-			return 0
+			return false
 		}
 
 		i += 2
diff --git a/lib/mem/free_unix.q b/lib/mem/free_unix.q
index 2c61b78..8acf0df 100644
--- a/lib/mem/free_unix.q
+++ b/lib/mem/free_unix.q
@@ -1,5 +1,5 @@
 import sys
 
-free(address []any) -> int {
-	return sys.munmap(address-8, len(address)+8)
+free(address []any) {
+	sys.munmap(address-8, len(address)+8)
 }
\ No newline at end of file
diff --git a/lib/mem/free_windows.q b/lib/mem/free_windows.q
index 1bb258a..3cf8a91 100644
--- a/lib/mem/free_windows.q
+++ b/lib/mem/free_windows.q
@@ -2,6 +2,6 @@ extern kernel32 {
 	VirtualFree(address *any, size uint, type uint32) -> bool
 }
 
-free(address []any) -> int {
-	return kernel32.VirtualFree(address-8, len(address)+8, mem.decommit)
+free(address []any) {
+	kernel32.VirtualFree(address-8, len(address)+8, mem.decommit)
 }
\ No newline at end of file
diff --git a/src/core/CompileCondition.go b/src/core/CompileCondition.go
index a0c8ffe..0e41f82 100644
--- a/src/core/CompileCondition.go
+++ b/src/core/CompileCondition.go
@@ -1,8 +1,11 @@
 package core
 
 import (
+	"git.urbach.dev/cli/q/src/asm"
+	"git.urbach.dev/cli/q/src/errors"
 	"git.urbach.dev/cli/q/src/expression"
 	"git.urbach.dev/cli/q/src/token"
+	"git.urbach.dev/cli/q/src/types"
 )
 
 // CompileCondition inserts code to jump to the start label or end label depending on the truth of the condition.
@@ -62,7 +65,26 @@ func (f *Function) CompileCondition(condition *expression.Expression, successLab
 
 		return err
 
-	default:
+	case token.Call:
+		typ, err := f.CompileCall(condition)
+
+		if err != nil {
+			return err
+		}
+
+		if len(typ) == 0 {
+			return errors.New(errors.UntypedExpression, f.File, condition.Token.Position)
+		}
+
+		if !types.Is(typ[0], types.Bool) {
+			return errors.New(&errors.TypeMismatch{Encountered: typ[0].Name(), Expected: types.Bool.Name()}, f.File, condition.Token.Position)
+		}
+
+		f.RegisterNumber(asm.COMPARE, f.CPU.Output[0], 0)
+		f.Jump(asm.JE, failLabel)
+		return nil
+
+	case token.Equal, token.NotEqual, token.Greater, token.Less, token.GreaterEqual, token.LessEqual:
 		err := f.Compare(condition)
 
 		if condition.Parent == nil {
@@ -70,5 +92,8 @@ func (f *Function) CompileCondition(condition *expression.Expression, successLab
 		}
 
 		return err
+
+	default:
+		return errors.New(errors.InvalidCondition, f.File, condition.Token.Position)
 	}
 }
diff --git a/src/core/Evaluate.go b/src/core/Evaluate.go
index 5e36fec..7189cf6 100644
--- a/src/core/Evaluate.go
+++ b/src/core/Evaluate.go
@@ -1,6 +1,7 @@
 package core
 
 import (
+	"git.urbach.dev/cli/q/src/ast"
 	"git.urbach.dev/cli/q/src/cpu"
 	"git.urbach.dev/cli/q/src/errors"
 	"git.urbach.dev/cli/q/src/expression"
@@ -24,6 +25,16 @@ func (f *Function) Evaluate(expr *expression.Expression) (types.Type, cpu.Regist
 		}
 	}
 
+	if ast.IsFunctionCall(expr) {
+		types, err := f.CompileCall(expr)
+
+		if err != nil {
+			return nil, 0, false, err
+		}
+
+		return types[0], f.CPU.Output[0], false, nil
+	}
+
 	tmp := f.NewRegister()
 	typ, err := f.ExpressionToRegister(expr, tmp)
 	return typ, tmp, true, err
diff --git a/src/core/TokenToRegister.go b/src/core/TokenToRegister.go
index a8128eb..e05d9e8 100644
--- a/src/core/TokenToRegister.go
+++ b/src/core/TokenToRegister.go
@@ -16,6 +16,17 @@ func (f *Function) TokenToRegister(t token.Token, register cpu.Register) (types.
 	switch t.Kind {
 	case token.Identifier:
 		name := t.Text(f.File.Bytes)
+
+		if name == "true" {
+			f.RegisterNumber(asm.MOVE, register, 1)
+			return types.Bool, nil
+		}
+
+		if name == "false" {
+			f.RegisterNumber(asm.MOVE, register, 0)
+			return types.Bool, nil
+		}
+
 		variable, function := f.Identifier(name)
 
 		if variable != nil {
diff --git a/src/errors/Common.go b/src/errors/Common.go
index 3b1d665..f5f4f50 100644
--- a/src/errors/Common.go
+++ b/src/errors/Common.go
@@ -10,6 +10,7 @@ var (
 	ExpectedStructName         = &Base{"Expected struct name"}
 	ExpectedDLLName            = &Base{"Expected DLL name"}
 	InvalidNumber              = &Base{"Invalid number"}
+	InvalidCondition           = &Base{"Invalid condition"}
 	InvalidExpression          = &Base{"Invalid expression"}
 	InvalidRune                = &Base{"Invalid rune"}
 	MissingBlockStart          = &Base{"Missing '{'"}
diff --git a/src/types/Common.go b/src/types/Common.go
index 3d2a870..8cab280 100644
--- a/src/types/Common.go
+++ b/src/types/Common.go
@@ -4,6 +4,7 @@ var (
 	Any        = &Base{name: "any", size: 0}
 	AnyArray   = &Array{Of: Any}
 	AnyPointer = &Pointer{To: Any}
+	Bool       = &Base{name: "bool", size: 1}
 	Int64      = &Base{name: "int64", size: 8}
 	Int32      = &Base{name: "int32", size: 4}
 	Int16      = &Base{name: "int16", size: 2}
@@ -14,7 +15,6 @@ var (
 )
 
 var (
-	Bool   = Int
 	Byte   = UInt8
 	Int    = Int64
 	Float  = Float64
diff --git a/src/types/Is.go b/src/types/Is.go
index 4134701..1629454 100644
--- a/src/types/Is.go
+++ b/src/types/Is.go
@@ -25,8 +25,12 @@ func Is(a Type, b Type) bool {
 		return true
 	}
 
-	// Temporary hack for implicit casts
-	if a.Size() > b.Size() {
+	// Temporary hacks
+	if a == Int32 && b == Int64 {
+		return true
+	}
+
+	if a == Int64 && b == Int32 {
 		return true
 	}
 
diff --git a/tests/errors/InvalidCondition.q b/tests/errors/InvalidCondition.q
new file mode 100644
index 0000000..8d76be8
--- /dev/null
+++ b/tests/errors/InvalidCondition.q
@@ -0,0 +1,3 @@
+main() {
+	if 42 {}
+}
\ No newline at end of file
diff --git a/tests/errors_test.go b/tests/errors_test.go
index c31056e..6b10e3f 100644
--- a/tests/errors_test.go
+++ b/tests/errors_test.go
@@ -22,6 +22,7 @@ var errs = []struct {
 	{"ExpectedIfBeforeElse2.q", errors.ExpectedIfBeforeElse},
 	{"ExpectedStructName.q", errors.ExpectedStructName},
 	{"ExpectedPackageName.q", errors.ExpectedPackageName},
+	{"InvalidCondition.q", errors.InvalidCondition},
 	{"InvalidInstructionCall.q", &errors.InvalidInstruction{Instruction: "sys.write"}},
 	{"InvalidInstructionExpression.q", &errors.InvalidInstruction{Instruction: "2+3"}},
 	{"InvalidInstructionIdentifier.q", &errors.InvalidInstruction{Instruction: "abc"}},