diff --git a/build/context.go b/build/context.go
index cbfc639c..2373ec0a 100644
--- a/build/context.go
+++ b/build/context.go
@@ -56,6 +56,12 @@ func (c *Context) Package(path string) {
 	c.pkg = pkg
 }
 
+// Include adds an include pre-processor directive for the provided path, if it
+// is not already present.
+func (c *Context) Include(path string) {
+	c.file.Include(path)
+}
+
 // Constraints sets build constraints for the file.
 func (c *Context) Constraints(t buildtags.ConstraintsConvertable) {
 	cs := t.ToConstraints()
@@ -160,6 +166,11 @@ func (c *Context) Label(name string) {
 	c.activefunc().AddLabel(ir.Label(name))
 }
 
+// Preprocessor adds a preprocessor macro to the active function.
+func (c *Context) Preprocessor(macro string) {
+	c.activefunc().AddPreprocessor(macro)
+}
+
 // Comment adds comment lines to the active function.
 func (c *Context) Comment(lines ...string) {
 	c.activefunc().AddComment(lines...)
diff --git a/build/global.go b/build/global.go
index 3a1690c1..c77de6f2 100644
--- a/build/global.go
+++ b/build/global.go
@@ -55,9 +55,16 @@ func Generate() {
 	}
 }
 
+// Include adds an include pre-processor directive for the provided path to the
+// current file, if it is not already present.
+func Include(path string) { ctx.Include(path) }
+
 // Package sets the package the generated file will belong to. Required to be able to reference types in the package.
 func Package(path string) { ctx.Package(path) }
 
+// Preprocessor adds a pre-processor macro to the current function.
+func Preprocessor(macro string) { ctx.Preprocessor(macro) }
+
 // Constraints sets build constraints for the file.
 func Constraints(t buildtags.ConstraintsConvertable) { ctx.Constraints(t) }
 
diff --git a/ir/ir.go b/ir/ir.go
index 871d4881..117d676f 100644
--- a/ir/ir.go
+++ b/ir/ir.go
@@ -2,7 +2,6 @@ package ir
 
 import (
 	"errors"
-
 	"github.com/mmcloughlin/avo/attr"
 	"github.com/mmcloughlin/avo/buildtags"
 	"github.com/mmcloughlin/avo/gotypes"
@@ -15,6 +14,16 @@ type Node interface {
 	node()
 }
 
+// Preprocessor macro within a function.
+type Preprocessor string
+
+func (p Preprocessor) node() {}
+
+// NewPreprocessor builds a Preprocessor from the provided macro string.
+func NewPreprocessor(macro string) Preprocessor {
+	return Preprocessor(macro)
+}
+
 // Label within a function.
 type Label string
 
@@ -162,6 +171,17 @@ func (f *File) Functions() []*Function {
 	return fns
 }
 
+// Include adds an include pre-processor directive for the provided path, if it
+// is not already present.
+func (f *File) Include(path string) {
+	for _, p := range f.Includes {
+		if p == path {
+			return
+		}
+	}
+	f.Includes = append(f.Includes, path)
+}
+
 // Pragma represents a function compiler directive.
 type Pragma struct {
 	Directive string
@@ -230,6 +250,11 @@ func (f *Function) AddLabel(l Label) {
 	f.AddNode(l)
 }
 
+// AddPreprocessor adds a pre-processor macro to f.
+func (f *Function) AddPreprocessor(macro string) {
+	f.AddNode(NewPreprocessor(macro))
+}
+
 // AddComment adds comment lines to f.
 func (f *Function) AddComment(lines ...string) {
 	f.AddNode(NewComment(lines...))
diff --git a/pass/cfg.go b/pass/cfg.go
index d5f6ea4e..3742fdfd 100644
--- a/pass/cfg.go
+++ b/pass/cfg.go
@@ -49,14 +49,13 @@ func CFG(fn *ir.Function) error {
 		// If it's a branch, locate the target.
 		if cur.IsBranch {
 			lbl := cur.TargetLabel()
-			if lbl == nil {
-				return errors.New("no label for branch instruction")
+			if lbl != nil {
+				target, found := fn.LabelTarget[*lbl]
+				if !found {
+					return fmt.Errorf("unknown label %q", *lbl)
+				}
+				cur.Succ = append(cur.Succ, target)
 			}
-			target, found := fn.LabelTarget[*lbl]
-			if !found {
-				return fmt.Errorf("unknown label %q", *lbl)
-			}
-			cur.Succ = append(cur.Succ, target)
 		}
 
 		// Otherwise, could continue to the following instruction.
diff --git a/printer/goasm.go b/printer/goasm.go
index 23f5b2f7..6bdf0579 100644
--- a/printer/goasm.go
+++ b/printer/goasm.go
@@ -111,6 +111,9 @@ func (p *goasm) function(f *ir.Function) {
 			for _, line := range n.Lines {
 				p.Printf("\t// %s\n", line)
 			}
+		case ir.Preprocessor:
+			p.flush()
+			p.Printf("#%s\n", string(n))
 		default:
 			panic("unexpected node type")
 		}
diff --git a/printer/goasm_test.go b/printer/goasm_test.go
index e8b4fe1e..2bf17575 100644
--- a/printer/goasm_test.go
+++ b/printer/goasm_test.go
@@ -135,3 +135,51 @@ func TestOpcodeSuffixes(t *testing.T) {
 		"",
 	})
 }
+
+func TestPreprocessor(t *testing.T) {
+	ctx := build.NewContext()
+	ctx.Function("preprocessor")
+	ctx.SignatureExpr("func()")
+	ctx.Preprocessor("ifndef hasAVX2")
+	ctx.ADDQ(reg.RBX, reg.RAX)
+	ctx.VZEROUPPER()
+	ctx.Preprocessor("else")
+	ctx.ADDQ(reg.RAX, reg.RBX)
+	ctx.Preprocessor("endif")
+
+	AssertPrintsLines(t, ctx, printer.NewGoAsm, []string{
+		"// Code generated by avo. DO NOT EDIT.",
+		"",
+		"// func preprocessor()",
+		"TEXT ·preprocessor(SB), $0",
+		"#ifndef hasAVX2",
+		"\tADDQ BX, AX",
+		"\tVZEROUPPER",
+		"#else",
+		"\tADDQ AX, BX",
+		"#endif",
+		"",
+	})
+}
+
+func TestInclude(t *testing.T) {
+	ctx := build.NewContext()
+	ctx.Include("before.h")
+	ctx.Function("preprocessor")
+	ctx.SignatureExpr("func()")
+	ctx.Include("after.h")
+	ctx.VZEROUPPER()
+
+	AssertPrintsLines(t, ctx, printer.NewGoAsm, []string{
+		"// Code generated by avo. DO NOT EDIT.",
+		"",
+		"#include \"before.h\"",
+		"#include \"after.h\"",
+		"",
+		"// func preprocessor()",
+		"TEXT ·preprocessor(SB), $0",
+		"\tVZEROUPPER",
+		"",
+	})
+
+}