diff --git a/theme/components/button/button.css b/theme/components/button/button.css
index baf37796..e3d84e02 100644
--- a/theme/components/button/button.css
+++ b/theme/components/button/button.css
@@ -3,6 +3,7 @@
  * For licensing, see LICENSE.md.
  */
 
+@import "./mixins/_button.css";
 @import "../../mixins/_unselectable.css";
 @import "../tooltip/mixins/_tooltip.css";
 
diff --git a/theme/components/button/mixins/_button.css b/theme/components/button/mixins/_button.css
new file mode 100644
index 00000000..03ba7d2e
--- /dev/null
+++ b/theme/components/button/mixins/_button.css
@@ -0,0 +1,13 @@
+/*
+ * Copyright (c) 2003-2017, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md.
+ */
+
+/**
+ * A helper to define button–specific icon styles.
+ */
+@define-mixin ck-button-icon {
+	& .ck-icon {
+		@mixin-content;
+	}
+}