diff --git a/commons/src/commonTest/kotlin/com/vitorpamplona/amethyst/commons/richtext/UrlParserTest.kt b/commons/src/commonTest/kotlin/com/vitorpamplona/amethyst/commons/richtext/UrlParserTest.kt
index b9613c5cd..600c0f27f 100644
--- a/commons/src/commonTest/kotlin/com/vitorpamplona/amethyst/commons/richtext/UrlParserTest.kt
+++ b/commons/src/commonTest/kotlin/com/vitorpamplona/amethyst/commons/richtext/UrlParserTest.kt
@@ -281,6 +281,18 @@ class UrlParserTest {
             Urls(withScheme = emptySet()),
         )
 
+    /**
+     * Regression test for PR #1907: parsing a note whose content is only the Japanese phrase
+     * "今北産業" (a common internet abbreviation) must not throw a StringIndexOutOfBoundsException
+     * from Url.getPart() and must produce no detected URLs.
+     */
+    @Test
+    fun testImakitaSangyo() =
+        test(
+            "今北産業",
+            Urls(),
+        )
+
     @Test
     fun testHour() =
         test(
diff --git a/quartz/src/commonTest/kotlin/com/vitorpamplona/quartz/nip10Notes/urls/UrlsDetectorTest.kt b/quartz/src/commonTest/kotlin/com/vitorpamplona/quartz/nip10Notes/urls/UrlsDetectorTest.kt
index 0d526ab17..aae685bf2 100644
--- a/quartz/src/commonTest/kotlin/com/vitorpamplona/quartz/nip10Notes/urls/UrlsDetectorTest.kt
+++ b/quartz/src/commonTest/kotlin/com/vitorpamplona/quartz/nip10Notes/urls/UrlsDetectorTest.kt
@@ -41,4 +41,14 @@ class UrlsDetectorTest {
         assertContains(detectedLinks, "https://mysite.xyz")
         assertContains(detectedLinks, "https://myblog.xyz")
     }
+
+    /**
+     * Regression test for PR #1907: the Japanese phrase "今北産業" must not crash the URL
+     * detector with a StringIndexOutOfBoundsException and must return no URLs.
+     */
+    @Test
+    fun doesNotCrashOnJapaneseText() {
+        val detectedLinks = fastFindURLs("今北産業")
+        assertEquals(0, detectedLinks.size)
+    }
 }
diff --git a/quartz/src/commonTest/kotlin/com/vitorpamplona/quartz/utils/urldetector/UrlTest.kt b/quartz/src/commonTest/kotlin/com/vitorpamplona/quartz/utils/urldetector/UrlTest.kt
new file mode 100644
index 000000000..a29c5e99e
--- /dev/null
+++ b/quartz/src/commonTest/kotlin/com/vitorpamplona/quartz/utils/urldetector/UrlTest.kt
@@ -0,0 +1,64 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.quartz.utils.urldetector
+
+import com.vitorpamplona.quartz.utils.urldetector.detection.UrlDetector
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertNotNull
+
+/**
+ * Regression tests for PR #1907: StringIndexOutOfBoundsException in [Url.getPart] when
+ * processing the Japanese text "今北産業".
+ */
+class UrlTest {
+    /**
+     * Regression: detecting URLs in "今北産業" must not throw and must return no URLs.
+     */
+    @Test
+    fun detectingImakitaSangyoDoesNotThrow() {
+        val urls = UrlDetector("今北産業").detect()
+        assertEquals(0, urls.size)
+    }
+
+    /**
+     * Regression: constructing a Url with "今北産業" as the original string and a HOST
+     * marker at 0 with PORT at the string length (simulating a trimmed trailing character)
+     * must not throw StringIndexOutOfBoundsException when accessing any property.
+     *
+     * "今北産業" has length 4. PORT at 4 == length triggers the startIndex >= length guard
+     * added to getPart() in PR #1907.
+     */
+    @Test
+    fun urlPropertiesDoNotThrowForImakitaSangyoWithOutOfRangeMarker() {
+        val marker = UrlMarker()
+        marker.setIndex(UrlPart.HOST, 0)
+        marker.setIndex(UrlPart.PORT, 4) // == "今北産業".length
+        val url = marker.createUrl("今北産業")
+
+        assertNotNull(url.scheme)
+        assertNotNull(url.host)
+        assertNotNull(url.path)
+        assertNotNull(url.query)
+        assertNotNull(url.fragment)
+        assertEquals(-1, url.port) // getPart(PORT) returns null → -1
+    }
+}