diff --git a/at_rule.go b/at_rule.go
index 11b31ca..2fe2640 100644
--- a/at_rule.go
+++ b/at_rule.go
@@ -17,7 +17,7 @@ func (ar *atRule) WriteTo(w io.Writer) (int64, error) {
 
 	bf.WriteString(strings.TrimSpace(ar.ln.s))
 
-	if len(ar.sels) == 0 && len(ar.decs) == 0 {
+	if len(ar.sels) == 0 && len(ar.decs) == 0 && !ar.hasMixinDecs() && !ar.hasMixinSels() {
 		bf.WriteString(semicolon)
 		n, err := w.Write(bf.Bytes())
 		return int64(n), err
@@ -25,16 +25,25 @@ func (ar *atRule) WriteTo(w io.Writer) (int64, error) {
 
 	bf.WriteString(openBrace)
 
-	for _, dec := range ar.decs {
-		// Writing to the bytes.Buffer never returns an error.
-		dec.WriteTo(bf)
-	}
+	// Writing to the bytes.Buffer never returns an error.
+	ar.writeDecsTo(bf, nil)
 
 	for _, sel := range ar.sels {
 		// Writing to the bytes.Buffer never returns an error.
 		sel.WriteTo(bf)
 	}
 
+	// Write the mixin's selectors.
+	for _, mi := range ar.mixins {
+		sels, prms := mi.selsParams()
+
+		for _, sl := range sels {
+			sl.parent = ar
+			// Writing to the bytes.Buffer never returns an error.
+			sl.writeTo(bf, prms)
+		}
+	}
+
 	bf.WriteString(closeBrace)
 
 	n, err := w.Write(bf.Bytes())
diff --git a/e2e_test.go b/e2e_test.go
index d2133c5..f53ed26 100644
--- a/e2e_test.go
+++ b/e2e_test.go
@@ -11,7 +11,7 @@ import (
 func Test_e2e(t *testing.T) {
 	var wg sync.WaitGroup
 
-	for i := 1; i <= 10; i++ {
+	for i := 1; i <= 11; i++ {
 		idx := strconv.Itoa(i)
 
 		gcssPath := "test/e2e/actual/" + strings.Repeat("0", 4-len(idx)) + idx + ".gcss"
diff --git a/element_base.go b/element_base.go
index 3c41a84..c1f79d0 100644
--- a/element_base.go
+++ b/element_base.go
@@ -1,5 +1,10 @@
 package gcss
 
+import (
+	"bytes"
+	"io"
+)
+
 // elementBase holds the common fields of an element.
 type elementBase struct {
 	ln     *line
@@ -41,7 +46,7 @@ func (eBase *elementBase) Context() *context {
 	return eBase.ctx
 }
 
-// hasMixinDecs returns true if the selector has a mixin
+// hasMixinDecs returns true if the element has a mixin
 // which has declarations.
 func (eBase *elementBase) hasMixinDecs() bool {
 	for _, mi := range eBase.mixins {
@@ -53,6 +58,43 @@ func (eBase *elementBase) hasMixinDecs() bool {
 	return false
 }
 
+// hasMixinSels returns true if the element has a mixin
+// which has selectors.
+func (eBase *elementBase) hasMixinSels() bool {
+	for _, mi := range eBase.mixins {
+		if sels, _ := mi.selsParams(); len(sels) > 0 {
+			return true
+		}
+	}
+
+	return false
+}
+
+// writeDecsTo writes the element's declarations to w.
+func (eBase *elementBase) writeDecsTo(w io.Writer, params map[string]string) (int64, error) {
+	bf := new(bytes.Buffer)
+
+	// Write the declarations.
+	for _, dec := range eBase.decs {
+		// Writing to the bytes.Buffer never returns an error.
+		dec.writeTo(bf, params)
+	}
+
+	// Write the mixin's declarations.
+	for _, mi := range eBase.mixins {
+		decs, prms := mi.decsParams()
+
+		for _, dec := range decs {
+			// Writing to the bytes.Buffer never returns an error.
+			dec.writeTo(bf, prms)
+		}
+	}
+
+	n, err := w.Write(bf.Bytes())
+
+	return int64(n), err
+}
+
 // newElementBase creates and returns an element base.
 func newElementBase(ln *line, parent element) elementBase {
 	return elementBase{
diff --git a/selector.go b/selector.go
index ae0dabe..1824b3a 100644
--- a/selector.go
+++ b/selector.go
@@ -27,20 +27,8 @@ func (sel *selector) writeTo(w io.Writer, params map[string]string) (int64, erro
 		bf.WriteString(sel.names())
 		bf.WriteString(openBrace)
 
-		for _, dec := range sel.decs {
-			// Writing to the bytes.Buffer never returns an error.
-			dec.writeTo(bf, params)
-		}
-
-		// Write the mixin's declarations.
-		for _, mi := range sel.mixins {
-			decs, prms := mi.decsParams()
-
-			for _, dec := range decs {
-				// Writing to the bytes.Buffer never returns an error.
-				dec.writeTo(bf, prms)
-			}
-		}
+		// Writing to the bytes.Buffer never returns an error.
+		sel.writeDecsTo(bf, params)
 
 		bf.WriteString(closeBrace)
 	}
diff --git a/test/e2e/actual/0011.gcss b/test/e2e/actual/0011.gcss
new file mode 100644
index 0000000..7f62faf
--- /dev/null
+++ b/test/e2e/actual/0011.gcss
@@ -0,0 +1,55 @@
+// At-rules which include mixins
+$color: black
+
+$mixin-for-media-1($font-size)
+  font-size: $font-size
+
+$mixin-for-media-2($background)
+  html
+    background: $background
+    color: $color
+
+$mixin-for-media-3()
+  h1
+    color: red
+
+$mixin-for-page($margin)
+  margin: $margin
+
+$mixin-for-font-face()
+  font-family: "Example Font"
+  src: url("http://www.example.com/fonts/example")
+
+@media screen, projection
+  $mixin-for-media-1(13px)
+  $mixin-for-media-2(red)
+  body
+    max-width: 35em
+    margin: 0 auto
+    $mixin-for-media-3()
+
+@media screen, projection
+  $mixin-for-media-2(red)
+
+@media print
+  $mixin-for-media-1(13px)
+  $mixin-for-media-2(red)
+  body
+    max-width: 35em
+    margin: 0 auto
+    $mixin-for-media-3()
+
+@page
+  $mixin-for-page(2.5cm)
+
+@page :left
+  $mixin-for-page(2.5cm)
+
+@page :right
+  $mixin-for-page(2.5cm)
+
+@page :first
+  $mixin-for-page(2.5cm)
+
+@font-face
+  $mixin-for-font-face()
diff --git a/test/e2e/expected/0011.css b/test/e2e/expected/0011.css
new file mode 100644
index 0000000..91bb9dd
--- /dev/null
+++ b/test/e2e/expected/0011.css
@@ -0,0 +1 @@
+@media screen, projection{font-size:13px;body{max-width:35em;margin:0 auto;}body h1{color:red;}html{background:red;color:black;}}@media screen, projection{html{background:red;color:black;}}@media print{font-size:13px;body{max-width:35em;margin:0 auto;}body h1{color:red;}html{background:red;color:black;}}@page{margin:2.5cm;}@page :left{margin:2.5cm;}@page :right{margin:2.5cm;}@page :first{margin:2.5cm;}@font-face{font-family:"Example Font";src:url("http://www.example.com/fonts/example");}