diff --git a/google-http-client/src/main/java/com/google/api/client/http/UriTemplate.java b/google-http-client/src/main/java/com/google/api/client/http/UriTemplate.java
index d6095c4b4..f8f078da3 100644
--- a/google-http-client/src/main/java/com/google/api/client/http/UriTemplate.java
+++ b/google-http-client/src/main/java/com/google/api/client/http/UriTemplate.java
@@ -320,12 +320,30 @@ public static String expand(
   }
 
   private static String getSimpleValue(String name, String value, CompositeOutput compositeOutput) {
+    validatePathSegments(name, value, compositeOutput);
     if (compositeOutput.requiresVarAssignment()) {
       return String.format("%s=%s", name, compositeOutput.getEncodedValue(value));
     }
     return compositeOutput.getEncodedValue(value);
   }
 
+  private static void validatePathSegments(
+      String name, String value, CompositeOutput compositeOutput) {
+    if (compositeOutput == CompositeOutput.SIMPLE) {
+      if (".".equals(value) || "..".equals(value)) {
+        throw new IllegalArgumentException(String.format("Invalid value %s for %s.", value, name));
+      }
+    } else if (compositeOutput == CompositeOutput.PLUS) {
+      for (String segment : Splitter.on('/').split(value)) {
+        if (".".equals(segment) || "..".equals(segment)) {
+          throw new IllegalArgumentException(
+              String.format(
+                  "Value for %s must not contain segments that are exactly . or ..", name));
+        }
+      }
+    }
+  }
+
   /**
    * Expand the template of a composite list property. Eg: If d := ["red", "green", "blue"] then
    * {/d*} is expanded to "/red/green/blue"
diff --git a/google-http-client/src/test/java/com/google/api/client/http/UriTemplateTest.java b/google-http-client/src/test/java/com/google/api/client/http/UriTemplateTest.java
index 9fc90ba85..061e42010 100644
--- a/google-http-client/src/test/java/com/google/api/client/http/UriTemplateTest.java
+++ b/google-http-client/src/test/java/com/google/api/client/http/UriTemplateTest.java
@@ -15,6 +15,7 @@
 package com.google.api.client.http;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertThrows;
 import static org.junit.Assert.assertTrue;
 
 import com.google.api.client.util.Value;
@@ -433,4 +434,54 @@ public void testExpandTemplates_reservedExpansion_mapWithMixedEncodedInput() {
     assertEquals(
         "#key1,val1%2F,key2,val2%2F,key3,val%20", UriTemplate.expand("{#keys}", variables, false));
   }
+
+  @Test
+  public void testExpandTemplates_rejectsDotSegmentsInSimpleExpansion() {
+    Map<String, Object> variables = Maps.newLinkedHashMap();
+    variables.put("webhook", "..");
+    IllegalArgumentException dotDotEx =
+        assertThrows(
+            IllegalArgumentException.class,
+            () -> UriTemplate.expand("v3/webhooks/{webhook}", variables, false));
+    assertEquals("Invalid value .. for webhook.", dotDotEx.getMessage());
+
+    variables.put("webhook", ".");
+    IllegalArgumentException dotEx =
+        assertThrows(
+            IllegalArgumentException.class,
+            () -> UriTemplate.expand("v3/webhooks/{webhook}", variables, false));
+    assertEquals("Invalid value . for webhook.", dotEx.getMessage());
+  }
+
+  @Test
+  public void testExpandTemplates_rejectsDotSegmentsInReservedExpansion() {
+    for (String invalidValue :
+        Arrays.asList(
+            "projects/p/locations/l/agents/a/sessions/..",
+            "projects/p/locations/l/agents/a/sessions/.",
+            "projects/sys-prod-123/databases/default/documents/doc-1/../../default",
+            "../escape-db",
+            "projects/sys-prod-123/databases/default/documents/doc-1/./child")) {
+      Map<String, Object> variables = Maps.newLinkedHashMap();
+      variables.put("name", invalidValue);
+      IllegalArgumentException ex =
+          assertThrows(
+              IllegalArgumentException.class,
+              () -> UriTemplate.expand("v1/{+name}", variables, false));
+      assertEquals(
+          "Value for name must not contain segments that are exactly . or ..", ex.getMessage());
+    }
+  }
+
+  @Test
+  public void testExpandTemplates_allowsSafeDotsInSimpleAndReservedExpansion() {
+    Map<String, Object> variables = Maps.newLinkedHashMap();
+    variables.put("name", "projects/sys-prod-123/databases/default/documents/my-file..txt");
+    assertEquals(
+        "v1/projects/sys-prod-123/databases/default/documents/my-file..txt",
+        UriTemplate.expand("v1/{+name}", variables, false));
+
+    variables.put("id", ".well-known");
+    assertEquals("v1/.well-known", UriTemplate.expand("v1/{id}", variables, false));
+  }
 }