diff --git a/pom.xml b/pom.xml
index 57e64d6..398c0a4 100644
--- a/pom.xml
+++ b/pom.xml
@@ -129,7 +129,7 @@
         <dependency>
             <groupId>ch.qos.logback</groupId>
             <artifactId>logback-classic</artifactId>
-            <version>1.3.12</version>
+            <version>1.2.13</version>
             <scope>test</scope>
         </dependency>
         <dependency>
diff --git a/src/main/java/ee/sk/mid/MidAuthenticationResponseValidator.java b/src/main/java/ee/sk/mid/MidAuthenticationResponseValidator.java
index d2f2b2b..61b226f 100644
--- a/src/main/java/ee/sk/mid/MidAuthenticationResponseValidator.java
+++ b/src/main/java/ee/sk/mid/MidAuthenticationResponseValidator.java
@@ -193,7 +193,7 @@ private boolean isCertificateTrusted(X509Certificate certificate) {
                 certificate.verify(trustedCACertificate.getPublicKey());
                 return true;
             } catch (GeneralSecurityException e) {
-                logger.warn("Error verifying signer's certificate: " + certificate.getSubjectDN() + " against CA certificate: " + trustedCACertificate.getSubjectDN(), e);
+                logger.debug("Error verifying signer's certificate: " + certificate.getSubjectDN() + " against CA certificate: " + trustedCACertificate.getSubjectDN(), e);
             }
         }
         return false;
diff --git a/src/test/java/ee/sk/mid/AuthenticationResponseValidatorTest.java b/src/test/java/ee/sk/mid/AuthenticationResponseValidatorTest.java
index 8c0d537..0e13cb0 100644
--- a/src/test/java/ee/sk/mid/AuthenticationResponseValidatorTest.java
+++ b/src/test/java/ee/sk/mid/AuthenticationResponseValidatorTest.java
@@ -43,11 +43,17 @@
 import static org.hamcrest.Matchers.is;
 import static org.hamcrest.Matchers.notNullValue;
 
+import java.util.Arrays;
 import java.security.cert.X509Certificate;
 import java.util.Collections;
 
+import ch.qos.logback.classic.Level;
+import ch.qos.logback.classic.Logger;
+import ch.qos.logback.classic.spi.ILoggingEvent;
+import ch.qos.logback.core.read.ListAppender;
 import ee.sk.mid.exception.MidInternalErrorException;
 import org.junit.Test;
+import org.slf4j.LoggerFactory;
 
 public class AuthenticationResponseValidatorTest {
 
@@ -95,6 +101,37 @@ public void validate_whenCertificateNotTrusted_shouldReturnCertificateNotTrusted
         assertThat(authenticationResult.getErrors(), hasItem(equalTo("Certificate that was returned is not signed by CA that is configured as trusted in mid-rest-java-client")));
     }
 
+    @Test
+    public void validate_whenTrustedCaIterationFailsInitially_shouldLogAtDebugLevel() {
+        X509Certificate wrongCaCertificate = fileToX509Certificate("/trusted_certificates/TEST_of_ESTEID-SK_2011.pem.crt");
+        X509Certificate correctCaCertificate = fileToX509Certificate("/trusted_certificates/TEST_of_ESTEID-SK_2015.pem.crt");
+        MidAuthenticationResponseValidator validator = new MidAuthenticationResponseValidator(Arrays.asList(wrongCaCertificate, correctCaCertificate));
+
+        Logger validatorLogger = (Logger) LoggerFactory.getLogger(MidAuthenticationResponseValidator.class);
+        Level previousLevel = validatorLogger.getLevel();
+        validatorLogger.setLevel(Level.DEBUG);
+        ListAppender<ILoggingEvent> listAppender = new ListAppender<>();
+        listAppender.start();
+        validatorLogger.addAppender(listAppender);
+        try {
+            MidAuthenticationResult authenticationResult = validator.validate(createValidMobileIdAuthentication());
+            assertThat(authenticationResult.isValid(), is(true));
+        } finally {
+            validatorLogger.detachAppender(listAppender);
+            validatorLogger.setLevel(previousLevel);
+        }
+
+        boolean hasDebugLog = listAppender.list.stream()
+                .anyMatch(event -> event.getLevel().equals(Level.DEBUG)
+                        && event.getFormattedMessage().contains("Error verifying signer's certificate"));
+        boolean hasWarnLog = listAppender.list.stream()
+                .anyMatch(event -> event.getLevel().equals(Level.WARN)
+                        && event.getFormattedMessage().contains("Error verifying signer's certificate"));
+
+        assertThat(hasDebugLog, is(true));
+        assertThat(hasWarnLog, is(false));
+    }
+
     @Test
     public void validate_whenResultLowerCase_shouldReturnValidAuthenticationResult() throws Exception {
         MidAuthentication authentication = MidAuthentication.newBuilder()