diff --git a/src/wp-includes/post-template.php b/src/wp-includes/post-template.php
index 22acff563f..64e6e049ea 100644
--- a/src/wp-includes/post-template.php
+++ b/src/wp-includes/post-template.php
@@ -471,11 +471,16 @@ function get_post_class( $class = '', $post_id = null ) {
 					continue;
 				}
 
+				$term_class = sanitize_html_class( $term->slug, $term->term_id );
+				if ( is_numeric( $term_class ) || ! trim( $term_class, '-' ) ) {
+					$term_class = $term->term_id;
+				}
+
 				// 'post_tag' uses the 'tag' prefix for backward compatibility.
 				if ( 'post_tag' == $taxonomy ) {
-					$classes[] = 'tag-' . sanitize_html_class( $term->slug, $term->term_id );
+					$classes[] = 'tag-' . $term_class;
 				} else {
-					$classes[] = sanitize_html_class( $taxonomy . '-' . $term->slug, $taxonomy . '-' . $term->term_id );
+					$classes[] = sanitize_html_class( $taxonomy . '-' . $term_class, $taxonomy . '-' . $term->term_id );
 				}
 			}
 		}
@@ -588,21 +593,36 @@ function get_body_class( $class = '' ) {
 			$cat = $wp_query->get_queried_object();
 			$classes[] = 'category';
 			if ( isset( $cat->term_id ) ) {
-				$classes[] = 'category-' . sanitize_html_class( $cat->slug, $cat->term_id );
+				$cat_class = sanitize_html_class( $cat->slug, $cat->term_id );
+				if ( is_numeric( $cat_class ) || ! trim( $cat_class, '-' ) ) {
+					$cat_class = $cat->term_id;
+				}
+
+				$classes[] = 'category-' . $cat_class;
 				$classes[] = 'category-' . $cat->term_id;
 			}
 		} elseif ( is_tag() ) {
-			$tags = $wp_query->get_queried_object();
+			$tag = $wp_query->get_queried_object();
 			$classes[] = 'tag';
-			if ( isset( $tags->term_id ) ) {
-				$classes[] = 'tag-' . sanitize_html_class( $tags->slug, $tags->term_id );
-				$classes[] = 'tag-' . $tags->term_id;
+			if ( isset( $tag->term_id ) ) {
+				$tag_class = sanitize_html_class( $tag->slug, $tag->term_id );
+				if ( is_numeric( $tag_class ) || ! trim( $tag_class, '-' ) ) {
+					$tag_class = $tag->term_id;
+				}
+
+				$classes[] = 'tag-' . $tag_class;
+				$classes[] = 'tag-' . $tag->term_id;
 			}
 		} elseif ( is_tax() ) {
 			$term = $wp_query->get_queried_object();
 			if ( isset( $term->term_id ) ) {
+				$term_class = sanitize_html_class( $term->slug, $term->term_id );
+				if ( is_numeric( $term_class ) || ! trim( $term_class, '-' ) ) {
+					$term_class = $term->term_id;
+				}
+
 				$classes[] = 'tax-' . sanitize_html_class( $term->taxonomy );
-				$classes[] = 'term-' . sanitize_html_class( $term->slug, $term->term_id );
+				$classes[] = 'term-' . $term_class;
 				$classes[] = 'term-' . $term->term_id;
 			}
 		}
diff --git a/tests/phpunit/tests/post/getBodyClass.php b/tests/phpunit/tests/post/getBodyClass.php
new file mode 100644
index 0000000000..38686b30b5
--- /dev/null
+++ b/tests/phpunit/tests/post/getBodyClass.php
@@ -0,0 +1,81 @@
+<?php
+
+/**
+ * @group post
+ * @covers ::get_body_class
+ */
+class Tests_Post_GetBodyClass extends WP_UnitTestCase {
+	protected $post_id;
+
+	public function setUp() {
+		parent::setUp();
+		$this->post_id = $this->factory->post->create();
+	}
+
+	/**
+	 * @ticket 30883
+	 */
+	public function test_with_utf8_category_slugs() {
+		$cat_id1 = $this->factory->category->create( array( 'name' => 'Первая рубрика' ) );
+		$cat_id2 = $this->factory->category->create( array( 'name' => 'Вторая рубрика' ) );
+		$cat_id3 = $this->factory->category->create( array( 'name' => '25кадр' ) );
+		wp_set_post_terms( $this->post_id, array( $cat_id1, $cat_id2, $cat_id3 ), 'category' );
+
+		$this->go_to( home_url( "?cat=$cat_id1" ) );
+		$this->assertContains( "category-$cat_id1", get_body_class() );
+
+		$this->go_to( home_url( "?cat=$cat_id2" ) );
+		$this->assertContains( "category-$cat_id2", get_body_class() );
+
+		$this->go_to( home_url( "?cat=$cat_id3" ) );
+		$this->assertContains( "category-$cat_id3", get_body_class() );
+	}
+
+	/**
+	 * @ticket 30883
+	 */
+	public function test_with_utf8_tag_slugs() {
+		$tag_id1 = $this->factory->tag->create( array( 'name' => 'Первая метка' ) );
+		$tag_id2 = $this->factory->tag->create( array( 'name' => 'Вторая метка' ) );
+		$tag_id3 = $this->factory->tag->create( array( 'name' => '25кадр' ) );
+		wp_set_post_terms( $this->post_id, array( $tag_id1, $tag_id2, $tag_id3 ), 'post_tag' );
+
+		$tag1 = get_term( $tag_id1, 'post_tag' );
+		$tag2 = get_term( $tag_id2, 'post_tag' );
+		$tag3 = get_term( $tag_id3, 'post_tag' );
+
+		$this->go_to( home_url( "?tag={$tag1->slug}" ) );
+		$this->assertContains( "tag-$tag_id1", get_body_class() );
+
+		$this->go_to( home_url( "?tag={$tag2->slug}" ) );
+		$this->assertContains( "tag-$tag_id2", get_body_class() );
+
+		$this->go_to( home_url( "?tag={$tag3->slug}" ) );
+		$this->assertContains( "tag-$tag_id3", get_body_class() );
+	}
+
+	/**
+	 * @ticket 30883
+	 */
+	public function test_with_utf8_term_slugs() {
+		register_taxonomy( 'wptests_tax', 'post' );
+		$term_id1 = $this->factory->term->create( array( 'taxonomy' => 'wptests_tax', 'name' => 'Первая метка' ) );
+		$term_id2 = $this->factory->term->create( array( 'taxonomy' => 'wptests_tax', 'name' => 'Вторая метка' ) );
+		$term_id3 = $this->factory->term->create( array( 'taxonomy' => 'wptests_tax', 'name' => '25кадр' ) );
+		wp_set_post_terms( $this->post_id, array( $term_id1, $term_id2, $term_id3 ), 'wptests_tax' );
+
+		$term1 = get_term( $term_id1, 'wptests_tax' );
+		$term2 = get_term( $term_id2, 'wptests_tax' );
+		$term3 = get_term( $term_id3, 'wptests_tax' );
+
+		$this->go_to( home_url( "?wptests_tax={$term1->slug}" ) );
+		$this->assertContains( "term-$term_id1", get_body_class() );
+
+		$this->go_to( home_url( "?wptests_tax={$term2->slug}" ) );
+		$this->assertContains( "term-$term_id2", get_body_class() );
+
+		$this->go_to( home_url( "?wptests_tax={$term3->slug}" ) );
+		$this->assertContains( "term-$term_id3", get_body_class() );
+	}
+
+}
diff --git a/tests/phpunit/tests/post/getPostClass.php b/tests/phpunit/tests/post/getPostClass.php
index 9329f21be4..811de43ceb 100644
--- a/tests/phpunit/tests/post/getPostClass.php
+++ b/tests/phpunit/tests/post/getPostClass.php
@@ -53,6 +53,55 @@ class Tests_Post_GetPostClass extends WP_UnitTestCase {
 		$this->assertEquals( array( 'foo', 'bar' ),  get_post_class( array( 'foo', 'bar' ), null ) );
 	}
 
+	/**
+	 * @ticket 30883
+	 */
+	public function test_with_utf8_category_slugs() {
+		$cat_id1 = $this->factory->category->create( array( 'name' => 'Первая рубрика' ) );
+		$cat_id2 = $this->factory->category->create( array( 'name' => 'Вторая рубрика' ) );
+		$cat_id3 = $this->factory->category->create( array( 'name' => '25кадр' ) );
+		wp_set_post_terms( $this->post_id, array( $cat_id1, $cat_id2, $cat_id3 ), 'category' );
+
+		$found = get_post_class( '', $this->post_id );
+
+		$this->assertContains( "category-$cat_id1", $found );
+		$this->assertContains( "category-$cat_id2", $found );
+		$this->assertContains( "category-$cat_id3", $found );
+	}
+
+	/**
+	 * @ticket 30883
+	 */
+	public function test_with_utf8_tag_slugs() {
+		$tag_id1 = $this->factory->tag->create( array( 'name' => 'Первая метка' ) );
+		$tag_id2 = $this->factory->tag->create( array( 'name' => 'Вторая метка' ) );
+		$tag_id3 = $this->factory->tag->create( array( 'name' => '25кадр' ) );
+		wp_set_post_terms( $this->post_id, array( $tag_id1, $tag_id2, $tag_id3 ), 'post_tag' );
+
+		$found = get_post_class( '', $this->post_id );
+
+		$this->assertContains( "tag-$tag_id1", $found );
+		$this->assertContains( "tag-$tag_id2", $found );
+		$this->assertContains( "tag-$tag_id3", $found );
+	}
+
+	/**
+	 * @ticket 30883
+	 */
+	public function test_with_utf8_term_slugs() {
+		register_taxonomy( 'wptests_tax', 'post' );
+		$term_id1 = $this->factory->term->create( array( 'taxonomy' => 'wptests_tax', 'name' => 'Первая метка' ) );
+		$term_id2 = $this->factory->term->create( array( 'taxonomy' => 'wptests_tax', 'name' => 'Вторая метка' ) );
+		$term_id3 = $this->factory->term->create( array( 'taxonomy' => 'wptests_tax', 'name' => '25кадр' ) );
+		wp_set_post_terms( $this->post_id, array( $term_id1, $term_id2, $term_id3 ), 'wptests_tax' );
+
+		$found = get_post_class( '', $this->post_id );
+
+		$this->assertContains( "wptests_tax-$term_id1", $found );
+		$this->assertContains( "wptests_tax-$term_id2", $found );
+		$this->assertContains( "wptests_tax-$term_id3", $found );
+	}
+
 	/**
 	 * @group cache
 	 */