diff --git a/.github/dependabot.yml b/.github/dependabot.yml
index ab97e73..2d9fbea 100644
--- a/.github/dependabot.yml
+++ b/.github/dependabot.yml
@@ -25,3 +25,7 @@ updates:
       prefix: "fix"
       prefix-development: "chore"
       include: "scope"
+    ignore:
+      # idna 3.20 dropped transitional processing; pinned in pyproject.toml. (RSRMID-3125)
+      - dependency-name: "idna"
+        versions: [">=3.20"]
diff --git a/pyproject.toml b/pyproject.toml
index c5c14b7..de2fda5 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -28,7 +28,9 @@ dependencies = [
     "pytest-cov>=7.1.0",
     "twine>=7.0.0,<8",
     "black>=26.5.1,<27",
-    "idna>=3.19"
+    # idna 3.20 ignores uts46_remap(transitional=True), which IDNAProcessor relies on
+    # for the registries that still expect transitional processing. (RSRMID-3125)
+    "idna>=3.19,<3.20"
 ]
 classifiers = [
     "Programming Language :: Python :: 3",