diff --git a/docs/userguide/icu_data/buildtool.md b/docs/userguide/icu_data/buildtool.md
index 1741575d8b4..b0930bdf0a4 100644
--- a/docs/userguide/icu_data/buildtool.md
+++ b/docs/userguide/icu_data/buildtool.md
@@ -222,7 +222,7 @@ There are two concrete differences between additive and subtractive mode:
 |                         | Additive    | Subtractive |
 |-------------------------|-------------|-------------|
 | Default Feature Filter  | `"exclude"` | `"include"` |
-| Default Resource Filter | `"-/*"`     | `"+/*"`     |
+| Default Resource Filter | `"-/"`      | `"+/"`      |
 
 To enable additive mode, add the following setting to your filter file:
 
diff --git a/icu4c/source/python/icutools/databuilder/filtration.py b/icu4c/source/python/icutools/databuilder/filtration.py
index a74a7a743c6..9150eb28f20 100644
--- a/icu4c/source/python/icutools/databuilder/filtration.py
+++ b/icu4c/source/python/icutools/databuilder/filtration.py
@@ -319,9 +319,9 @@ class ResourceFilterInfo(object):
             )
         ]
         if self.strategy == "additive":
-            self.rules_by_file = [["-/*"] for _ in range(len(files))]
+            self.rules_by_file = [["-/"] for _ in range(len(files))]
         else:
-            self.rules_by_file = [["+/*"] for _ in range(len(files))]
+            self.rules_by_file = [["+/"] for _ in range(len(files))]
 
     def add_rules(self, file_filter, rules):
         for file, rule_list in zip(self.input_files, self.rules_by_file):
diff --git a/icu4c/source/python/icutools/databuilder/filtration_schema.json b/icu4c/source/python/icutools/databuilder/filtration_schema.json
index a68011f929d..ba027edce11 100644
--- a/icu4c/source/python/icutools/databuilder/filtration_schema.json
+++ b/icu4c/source/python/icutools/databuilder/filtration_schema.json
@@ -38,7 +38,7 @@
                         "type": "array",
                         "items": {
                             "type": "string",
-                            "pattern": "^[+-]/[\\S]+$"
+                            "pattern": "^[+-]/[\\S]*$"
                         }
                     }
                 },
diff --git a/icu4c/source/test/intltest/restsnew.cpp b/icu4c/source/test/intltest/restsnew.cpp
index 6f86709af88..0a6a121e67b 100644
--- a/icu4c/source/test/intltest/restsnew.cpp
+++ b/icu4c/source/test/intltest/restsnew.cpp
@@ -1270,13 +1270,11 @@ void NewResourceBundleTest::TestFilter() {
     assertEquals("fornia", fornia.getType(), URES_TABLE);
 
     {
+        // Filter: hawaii should not be included based on parent inheritance
         ResourceBundle hawaii = fornia.get("hawaii", status);
-        REQUIRE_SUCCESS(status);
-        assertEquals("hawaii", hawaii.getType(), URES_STRING);
-        assertEquals("hawaii", u"idaho", hawaii.getString(status));
-        REQUIRE_SUCCESS(status);
+        REQUIRE_ERROR(U_MISSING_RESOURCE_ERROR, status);
 
-        // Filter: illinois should not be included
+        // Filter: illinois should not be included based on direct rule
         ResourceBundle illinois = fornia.get("illinois", status);
         REQUIRE_ERROR(U_MISSING_RESOURCE_ERROR, status);
     }
@@ -1350,6 +1348,20 @@ void NewResourceBundleTest::TestFilter() {
             REQUIRE_ERROR(U_MISSING_RESOURCE_ERROR, status);
         }
     }
+
+    // Filter: northCarolina should be included based on direct rule,
+    // and so should its child, northDakota
+    ResourceBundle northCarolina = rb.get("northCarolina", status);
+    REQUIRE_SUCCESS(status);
+    assertEquals("northCarolina", northCarolina.getType(), URES_TABLE);
+
+    {
+        ResourceBundle northDakota = northCarolina.get("northDakota", status);
+        REQUIRE_SUCCESS(status);
+        assertEquals("northDakota", northDakota.getType(), URES_STRING);
+        assertEquals("northDakota", u"west-virginia", northDakota.getString(status));
+        REQUIRE_SUCCESS(status);
+    }
 }
 
 #if U_ENABLE_TRACING
diff --git a/icu4c/source/test/testdata/filters/filtertest.txt b/icu4c/source/test/testdata/filters/filtertest.txt
index 91c780146e5..f884dd124cd 100644
--- a/icu4c/source/test/testdata/filters/filtertest.txt
+++ b/icu4c/source/test/testdata/filters/filtertest.txt
@@ -1,6 +1,7 @@
 # Copyright (C) 2018 and later: Unicode, Inc. and others.
 # License & terms of use: http://www.unicode.org/copyright.html
 
+-/
 -/alabama
 +/alabama/alaska/arizona
 -/fornia/illinois
@@ -9,3 +10,4 @@
 +/mississippi/*/maine
 -/mississippi/*/iowa
 +/mississippi/louisiana/iowa
++/northCarolina
diff --git a/icu4c/source/test/testdata/filtertest.txt b/icu4c/source/test/testdata/filtertest.txt
index 4d9aeb50d55..1fbc71c01ec 100644
--- a/icu4c/source/test/testdata/filtertest.txt
+++ b/icu4c/source/test/testdata/filtertest.txt
@@ -34,4 +34,7 @@ filtertest {
             missouri {"new-york"}
         }
     }
+    northCarolina {
+        northDakota {"west-virginia"}
+    }
 }
diff --git a/icu4c/source/tools/genrb/filterrb.cpp b/icu4c/source/tools/genrb/filterrb.cpp
index d62d185d773..dcc02fc6210 100644
--- a/icu4c/source/tools/genrb/filterrb.cpp
+++ b/icu4c/source/tools/genrb/filterrb.cpp
@@ -23,6 +23,9 @@ ResKeyPath::ResKeyPath(const std::string& path, UErrorCode& status) {
         status = U_PARSE_ERROR;
         return;
     }
+    if (path.length() == 1) {
+        return;
+    }
     size_t i;
     size_t j = 0;
     while (true) {