diff --git a/changelog_unreleased/yaml/12305.md b/changelog_unreleased/yaml/12305.md
new file mode 100644
index 000000000..f989c6157
--- /dev/null
+++ b/changelog_unreleased/yaml/12305.md
@@ -0,0 +1,15 @@
+#### Fix unexpected deletion of block-literal lines which starts with U+3000 (#12305 by @Quramy)
+
+<!-- prettier-ignore -->
+```yaml
+# Input 
+block_with_ideographic_space: |
+  　line-content # This line starts with U+3000
+
+# Prettier stable
+block_with_ideographic_space: |
+
+// Prettier main
+block_with_ideographic_space: |
+  　line-content # This line starts with U+3000
+```
diff --git a/src/language-yaml/utils.js b/src/language-yaml/utils.js
index 82a4a354f..b1fde2d26 100644
--- a/src/language-yaml/utils.js
+++ b/src/language-yaml/utils.js
@@ -256,7 +256,7 @@ function getBlockValueLineContents(
   const leadingSpaceCount =
     node.indent === null
       ? ((match) => (match ? match[1].length : Number.POSITIVE_INFINITY))(
-          content.match(/^( *)\S/m)
+          content.match(/^( *)[^\n\r ]/m)
         )
       : node.indent - 1 + parentIndent;
 
diff --git a/tests/format/yaml/block-literal/jsfmt.spec.js b/tests/format/yaml/block-literal/jsfmt.spec.js
index bedc8dbb9..0c58d7617 100644
--- a/tests/format/yaml/block-literal/jsfmt.spec.js
+++ b/tests/format/yaml/block-literal/jsfmt.spec.js
@@ -1,2 +1,17 @@
-run_spec(__dirname, ["yaml"]);
-run_spec(__dirname, ["yaml"], { proseWrap: "always" });
+const { outdent } = require("outdent");
+
+const snippets = [
+  {
+    code: outdent`
+      block_with_ideographic_space: |
+        \u{3000}x
+    `,
+    output: outdent`
+      block_with_ideographic_space: |
+        \u{3000}x
+    `,
+  },
+].map((test) => ({ ...test, output: test.output + "\n" }));
+
+run_spec({ dirname: __dirname, snippets }, ["yaml"]);
+run_spec({ dirname: __dirname, snippets }, ["yaml"], { proseWrap: "always" });