diff --git a/buildutil.go b/buildutil.go
index 6876a5d..a51be7c 100644
--- a/buildutil.go
+++ b/buildutil.go
@@ -206,7 +206,6 @@ var emptyConstraint Constraint
 // A nil Constraint is safe to use and matches any build.Context.
 type Constraint struct {
 	expr constraint.Expr
-	tags map[string]bool
 }
 
 // NewConstraint returns a new Constraint for the given constraint.Expr and
@@ -215,7 +214,7 @@ func NewConstraint(expr constraint.Expr, tags map[string]bool) *Constraint {
 	if expr == nil && len(tags) == 0 {
 		return &emptyConstraint
 	}
-	return &Constraint{expr: expr, tags: tags}
+	return &Constraint{expr: expr}
 }
 
 // Expr returns the Constraint's constraint.Expr.
@@ -226,25 +225,13 @@ func (c *Constraint) Expr() constraint.Expr {
 	return c.expr
 }
 
-// Tags returns a copy of the Constraint's build tags.
-func (c *Constraint) Tags() map[string]bool {
-	if c == nil || len(c.tags) == 0 {
-		return nil
-	}
-	tags := make(map[string]bool, len(c.tags))
-	for k, v := range c.tags {
-		tags[k] = v
-	}
-	return tags
-}
-
 // Empty returns true if c has no build constraints. An empty Constraint
 // matches all files.
 func (c *Constraint) Empty() bool { return c == nil || c.expr == nil }
 
 // Eval reports whether build.Context ctxt matches the build constraint.
 func (c *Constraint) Eval(ctxt *build.Context) bool {
-	return c.Empty() || eval(ctxt, c.expr, c.tags)
+	return c.Empty() || eval(ctxt, c.expr, nil)
 }
 
 // ParseConstraint parses the build constraints of a Go source file, if any.
@@ -260,19 +247,11 @@ func ParseConstraint(ctxt *build.Context, filename string, src interface{}) (*Co
 	if err != nil {
 		return nil, err
 	}
-	tags := make(map[string]bool)
-	goodOSArchFile(ctxt, filepath.Base(filename), tags)
-	if _, _, err := shouldBuild(ctxt, data, tags); err != nil {
-		return nil, err
-	}
 	expr, err := parseBuildConstraint(data)
 	if err != nil {
 		return nil, err
 	}
-	if len(tags) == 0 {
-		tags = nil
-	}
-	return &Constraint{tags: tags, expr: expr}, nil
+	return &Constraint{expr: expr}, nil
 }
 
 func openReaderDirName(ctxt *build.Context, dir, name string, src interface{}) (io.ReadCloser, error) {
diff --git a/buildutil_test.go b/buildutil_test.go
index 612d8cc..07be47d 100644
--- a/buildutil_test.go
+++ b/buildutil_test.go
@@ -263,21 +263,6 @@ func TestShouldBuild(t *testing.T) {
 	}
 }
 
-func tagsEqual(m1, m2 map[string]bool) bool {
-	if len(m1) != len(m2) {
-		return false
-	}
-	if len(m1) == 0 {
-		return true
-	}
-	for k, v := range m1 {
-		if m2[k] != v {
-			return false
-		}
-	}
-	return true
-}
-
 func TestParseConstraint(t *testing.T) {
 	for _, tt := range shouldBuildTests {
 		t.Run(tt.name, func(t *testing.T) {
@@ -287,12 +272,12 @@ func TestParseConstraint(t *testing.T) {
 				t.Fatal(err)
 			}
 			shouldBuild := expr.Eval(ctx)
-			if shouldBuild != tt.shouldBuild || !tagsEqual(expr.tags, tt.tags) || err != tt.err {
+			if shouldBuild != tt.shouldBuild || err != tt.err {
 				t.Errorf("mismatch:\n"+
-					"have shouldBuild=%v, tags=%v, err=%v\n"+
-					"want shouldBuild=%v, tags=%v, err=%v",
-					shouldBuild, expr.tags, err,
-					tt.shouldBuild, tt.tags, tt.err)
+					"have shouldBuild=%v, err=%v\n"+
+					"want shouldBuild=%v, err=%v",
+					shouldBuild, err,
+					tt.shouldBuild, tt.err)
 			}
 		})
 	}
@@ -301,17 +286,10 @@ func TestParseConstraint(t *testing.T) {
 		ctxt := build.Default
 		ctxt.GOOS = "linux"
 		ctxt.GOARCH = "amd64"
-		want := map[string]bool{
-			"linux": true,
-			"amd64": true,
-		}
 		expr, err := ParseConstraint(&ctxt, "x_linux_amd64.go", []byte("package x\n"))
 		if err != nil {
 			t.Fatal(err)
 		}
-		if !tagsEqual(expr.tags, want) {
-			t.Errorf("Tags: got: %v want: %v", expr.tags, want)
-		}
 		if ok := expr.Eval(&ctxt); !ok {
 			t.Errorf("Eval: got: %t want: %t", ok, true)
 		}
@@ -323,9 +301,6 @@ func TestParseConstraint(t *testing.T) {
 		if err != nil {
 			t.Fatal(err)
 		}
-		if expr.tags != nil {
-			t.Errorf("Tags: got: %v want: %v", expr.tags, nil)
-		}
 		if expr.expr != nil {
 			t.Errorf("Expr: got: %v want: %v", expr.expr, nil)
 		}
@@ -334,32 +309,6 @@ func TestParseConstraint(t *testing.T) {
 		}
 	})
 
-	t.Run("Tags", func(t *testing.T) {
-		want := map[string]bool{"a": true, "b": true}
-		expr := NewConstraint(nil, want)
-		if tags := expr.Tags(); !tagsEqual(tags, want) {
-			if expr.tags != nil {
-				t.Errorf("Tags: got: %v want: %v", expr.tags, nil)
-			}
-		}
-		// Make sure we made a copy
-		tags := expr.Tags()
-		tags["aa"] = true
-		if !tagsEqual(expr.tags, want) {
-			t.Errorf("Tags: got: %v want: %v", expr.tags, nil)
-		}
-	})
-
-	t.Run("EmptyTags", func(t *testing.T) {
-		expr := NewConstraint(nil, map[string]bool{})
-		if expr != &emptyConstraint {
-			t.Error("Failed to return emptyConstraint when len(tags) == 0")
-		}
-		if expr.tags != nil {
-			t.Errorf("Tags: got: %v want: %v", expr.tags, nil)
-		}
-	})
-
 	t.Run("NilConstraint", func(t *testing.T) {
 		// Make sure a nil Constraint can be used
 		var expr *Constraint
@@ -369,9 +318,6 @@ func TestParseConstraint(t *testing.T) {
 		if expr.Expr() != nil {
 			t.Errorf("Expr: got: %v want: %v", expr.Expr(), nil)
 		}
-		if expr.Tags() != nil {
-			t.Errorf("Tags: got: %v want: %v", expr.Tags(), nil)
-		}
 		if !expr.Eval(nil) {
 			t.Errorf("Eval: got: %v want: %v", expr.Eval(nil), nil)
 		}