diff --git a/crates/usvg/src/parser/converter.rs b/crates/usvg/src/parser/converter.rs
index 38bdbdbff..09d7c2565 100644
--- a/crates/usvg/src/parser/converter.rs
+++ b/crates/usvg/src/parser/converter.rs
@@ -540,7 +540,16 @@ fn resolve_svg_size(svg: &SvgNode, opt: &Options) -> (Result<Size, Error>, bool)
             svg.convert_user_length(AId::Height, &state, def)
         };
 
-        Size::from_wh(w, h)
+        // If only one of height/width is not specified, its value should be
+        // computed from the other and the viewbox' aspect ratio.
+        match (
+            svg.attribute::<Length>(AId::Width),
+            svg.attribute::<Length>(AId::Height),
+        ) {
+            (Some(_), None) => Size::from_wh(w, vbox.height() * w / vbox.width()),
+            (None, Some(_)) => Size::from_wh(vbox.width() * h / vbox.height(), h),
+            (_, _) => Size::from_wh(w, h),
+        }
     } else {
         Size::from_wh(
             svg.convert_user_length(AId::Width, &state, def),
diff --git a/crates/usvg/tests/parser.rs b/crates/usvg/tests/parser.rs
index d2786d801..17eb4e89e 100644
--- a/crates/usvg/tests/parser.rs
+++ b/crates/usvg/tests/parser.rs
@@ -217,6 +217,34 @@ fn size_detection_5() {
     assert_eq!(tree.size(), usvg::Size::from_wh(100.0, 100.0).unwrap());
 }
 
+#[test]
+fn size_detection_6() {
+    let svg = "<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 10 10' width='30'/>";
+    let tree = usvg::Tree::from_str(&svg, &usvg::Options::default()).unwrap();
+    assert_eq!(tree.size(), usvg::Size::from_wh(30.0, 30.0).unwrap());
+}
+
+#[test]
+fn size_detection_7() {
+    let svg = "<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 10 20' width='30'/>";
+    let tree = usvg::Tree::from_str(&svg, &usvg::Options::default()).unwrap();
+    assert_eq!(tree.size(), usvg::Size::from_wh(30.0, 60.0).unwrap());
+}
+
+#[test]
+fn size_detection_8() {
+    let svg = "<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 10 10' height='30'/>";
+    let tree = usvg::Tree::from_str(&svg, &usvg::Options::default()).unwrap();
+    assert_eq!(tree.size(), usvg::Size::from_wh(30.0, 30.0).unwrap());
+}
+
+#[test]
+fn size_detection_9() {
+    let svg = "<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 10 20' height='30'/>";
+    let tree = usvg::Tree::from_str(&svg, &usvg::Options::default()).unwrap();
+    assert_eq!(tree.size(), usvg::Size::from_wh(15.0, 30.0).unwrap());
+}
+
 #[test]
 fn invalid_size_1() {
     let svg = "<svg width='0' height='0' viewBox='0 0 10 20' xmlns='http://www.w3.org/2000/svg'/>";