diff --git a/src/main/java/net/hostsharing/hsadminng/hs/office/contact/HsOfficeContactController.java b/src/main/java/net/hostsharing/hsadminng/hs/office/contact/HsOfficeContactController.java
index b45f070c..744a9342 100644
--- a/src/main/java/net/hostsharing/hsadminng/hs/office/contact/HsOfficeContactController.java
+++ b/src/main/java/net/hostsharing/hsadminng/hs/office/contact/HsOfficeContactController.java
@@ -40,12 +40,12 @@ public class HsOfficeContactController implements HsOfficeContactsApi {
             final String currentSubject,
             final String assumedRoles,
             final String caption,
-            final String emailAddress) {
+            final String emailAddressRegEx) {
         context.define(currentSubject, assumedRoles);
 
-        validate("caption, emailAddress").atMaxOne(caption, emailAddress);
-        final var entities = emailAddress != null
-             ? contactRepo.findContactByEmailAddress(emailAddress)
+        validate("caption, emailAddress").atMaxOne(caption, emailAddressRegEx);
+        final var entities = emailAddressRegEx != null
+             ? contactRepo.findContactByEmailAddressRegEx(emailAddressRegEx)
              : contactRepo.findContactByOptionalCaptionLike(caption);
 
 
diff --git a/src/main/java/net/hostsharing/hsadminng/hs/office/contact/HsOfficeContactRbacRepository.java b/src/main/java/net/hostsharing/hsadminng/hs/office/contact/HsOfficeContactRbacRepository.java
index 51c3990e..924f3277 100644
--- a/src/main/java/net/hostsharing/hsadminng/hs/office/contact/HsOfficeContactRbacRepository.java
+++ b/src/main/java/net/hostsharing/hsadminng/hs/office/contact/HsOfficeContactRbacRepository.java
@@ -4,6 +4,7 @@ import io.micrometer.core.annotation.Timed;
 import org.springframework.data.jpa.repository.Query;
 import org.springframework.data.repository.Repository;
 
+import jakarta.validation.ValidationException;
 import jakarta.validation.constraints.NotNull;
 import java.util.List;
 import java.util.Optional;
@@ -23,14 +24,22 @@ public interface HsOfficeContactRbacRepository extends Repository<HsOfficeContac
     List<HsOfficeContactRbacEntity> findContactByOptionalCaptionLike(String caption);
 
     @Query(value = """
-            SELECT c.* FROM hs_office.contact_rv c
-                WHERE jsonb_path_exists(c.emailaddresses, cast(:emailAddressExpression as jsonpath))
+            select c.* from hs_office.contact_rv c
+                where jsonb_path_exists(c.emailaddresses, cast(:emailAddressExpression as jsonpath))
             """, nativeQuery = true)
     @Timed("app.office.contacts.repo.findContactByEmailAddressImpl.rbac")
     List<HsOfficeContactRbacEntity> findContactByEmailAddressImpl(final String emailAddressExpression);
 
-    default  List<HsOfficeContactRbacEntity> findContactByEmailAddress(@NotNull final String emailAddress) {
-        return findContactByEmailAddressImpl("$.** ? (@ like_regex \"" + emailAddress.replace("%", ".*") + "\")");
+    default List<HsOfficeContactRbacEntity> findContactByEmailAddressRegEx(@NotNull final String emailAddress) {
+        return findContactByEmailAddressImpl("$.** ? (@ like_regex \"" + emailRegEx(emailAddress) + "\")");
+    }
+
+    static String emailRegEx(@NotNull String emailAddress) {
+        if (emailAddress.contains("'") || emailAddress.endsWith("\\") ) {
+            throw new ValidationException(
+                    "emailAddress contains invalid characters: " + emailAddress);
+        }
+        return emailAddress.replace("%", ".*"); // the JSON-matcher in PostgreSQL needs a wildcard
     }
 
     @Timed("app.office.contacts.repo.save.rbac")
diff --git a/src/main/resources/api-definition/hs-office/hs-office-contacts.yaml b/src/main/resources/api-definition/hs-office/hs-office-contacts.yaml
index 0dff9a63..022756d8 100644
--- a/src/main/resources/api-definition/hs-office/hs-office-contacts.yaml
+++ b/src/main/resources/api-definition/hs-office/hs-office-contacts.yaml
@@ -13,12 +13,13 @@ get:
           schema:
               type: string
           description: Beginning of caption to filter the results.
-        - name: emailAddress
+        - name: emailAddressRegEx
           in: query
           required: false
           schema:
               type: string
-          description: Beginning of email-address to filter the results, use '%' as wildcard.
+          description:
+              Regular-expression for an email-address to filter the results.
     responses:
         "200":
             description: OK
diff --git a/src/test/java/net/hostsharing/hsadminng/hs/office/contact/HsOfficeContactRbacRepositoryIntegrationTest.java b/src/test/java/net/hostsharing/hsadminng/hs/office/contact/HsOfficeContactRbacRepositoryIntegrationTest.java
index 5b59f3b6..6a7f45e3 100644
--- a/src/test/java/net/hostsharing/hsadminng/hs/office/contact/HsOfficeContactRbacRepositoryIntegrationTest.java
+++ b/src/test/java/net/hostsharing/hsadminng/hs/office/contact/HsOfficeContactRbacRepositoryIntegrationTest.java
@@ -193,7 +193,7 @@ class HsOfficeContactRbacRepositoryIntegrationTest extends ContextBasedTestWithC
             context("superuser-alex@hostsharing.net", null);
 
             // when
-            final var result = contactRepo.findContactByEmailAddress("%@secondcontact.example.com");
+            final var result = contactRepo.findContactByEmailAddressRegEx("@secondcontact.example.com");
 
             // then
             exactlyTheseContactsAreReturned(result, "second contact");
diff --git a/src/test/java/net/hostsharing/hsadminng/hs/office/contact/HsOfficeContactRbacRepositoryUnitTest.java b/src/test/java/net/hostsharing/hsadminng/hs/office/contact/HsOfficeContactRbacRepositoryUnitTest.java
new file mode 100644
index 00000000..d6c6574f
--- /dev/null
+++ b/src/test/java/net/hostsharing/hsadminng/hs/office/contact/HsOfficeContactRbacRepositoryUnitTest.java
@@ -0,0 +1,29 @@
+package net.hostsharing.hsadminng.hs.office.contact;
+
+import org.junit.jupiter.api.Test;
+
+import jakarta.validation.ValidationException;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.catchThrowable;
+
+class HsOfficeContactRbacRepositoryUnitTest {
+
+    @Test
+    void rejectsSingleQuoteInEmailAddressRegEx() {
+        final var throwable = catchThrowable( () ->
+                HsOfficeContactRbacRepository.emailRegEx("target@'example.org")
+        );
+
+        assertThat(throwable).isInstanceOf(ValidationException.class);
+    }
+
+    @Test
+    void rejectsTrailingBackslashInEmailAddressRegEx() {
+        final var throwable = catchThrowable( () ->
+                HsOfficeContactRbacRepository.emailRegEx("target@example.org\\")
+        );
+
+        assertThat(throwable).isInstanceOf(ValidationException.class);
+    }
+}