diff --git a/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/operations/CertifyOperation.java b/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/operations/CertifyOperation.java
index 3bd412c36..d231038da 100644
--- a/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/operations/CertifyOperation.java
+++ b/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/operations/CertifyOperation.java
@@ -94,6 +94,12 @@ public class CertifyOperation extends BaseOperation {
 
             try {
 
+                if (action.mMasterKeyId == parcel.mMasterKeyId) {
+                    log.add(LogType.MSG_CRT_ERROR_SELF, 2);
+                    certifyError += 1;
+                    continue;
+                }
+
                 if (action.mUserIds == null) {
                     log.add(LogType.MSG_CRT_CERTIFY_ALL, 2,
                             KeyFormattingUtils.convertKeyIdToHex(action.mMasterKeyId));
diff --git a/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/operations/results/OperationResult.java b/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/operations/results/OperationResult.java
index beafdcbb2..1388c0eac 100644
--- a/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/operations/results/OperationResult.java
+++ b/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/operations/results/OperationResult.java
@@ -587,6 +587,7 @@ public abstract class OperationResult implements Parcelable {
         MSG_CRT_CERTIFYING (LogLevel.DEBUG, R.string.msg_crt_certifying),
         MSG_CRT_CERTIFY_ALL (LogLevel.DEBUG, R.string.msg_crt_certify_all),
         MSG_CRT_CERTIFY_SOME (LogLevel.DEBUG, R.plurals.msg_crt_certify_some),
+        MSG_CRT_ERROR_SELF (LogLevel.ERROR, R.string.msg_crt_error_self),
         MSG_CRT_ERROR_MASTER_NOT_FOUND (LogLevel.ERROR, R.string.msg_crt_error_master_not_found),
         MSG_CRT_ERROR_NOTHING (LogLevel.ERROR, R.string.msg_crt_error_nothing),
         MSG_CRT_ERROR_UNLOCK (LogLevel.ERROR, R.string.msg_crt_error_unlock),
diff --git a/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/pgp/CanonicalizedSecretKey.java b/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/pgp/CanonicalizedSecretKey.java
index 42e59b3bc..6965ca7cb 100644
--- a/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/pgp/CanonicalizedSecretKey.java
+++ b/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/pgp/CanonicalizedSecretKey.java
@@ -300,6 +300,12 @@ public class CanonicalizedSecretKey extends CanonicalizedPublicKey {
         if (mPrivateKeyState == PRIVATE_KEY_STATE_LOCKED) {
             throw new PrivateKeyNotUnlockedException();
         }
+        if (!isMasterKey()) {
+            throw new AssertionError("tried to certify with non-master key, this is a programming error!");
+        }
+        if (publicKeyRing.getMasterKeyId() == getKeyId()) {
+            throw new AssertionError("key tried to self-certify, this is a programming error!");
+        }
 
         // create a signatureGenerator from the supplied masterKeyId and passphrase
         PGPSignatureGenerator signatureGenerator;
diff --git a/OpenKeychain/src/main/res/values/strings.xml b/OpenKeychain/src/main/res/values/strings.xml
index 16fd2691b..8dc708f1c 100644
--- a/OpenKeychain/src/main/res/values/strings.xml
+++ b/OpenKeychain/src/main/res/values/strings.xml
@@ -942,6 +942,7 @@
         <item quantity="one">"Certifying one user ID for key %2$s"</item>
         <item quantity="other">"Certifying %1$d user IDs for key %2$s"</item>
     </plurals>
+    <string name="msg_crt_error_self">"Cannot issue self-certificate like this!"</string>
     <string name="msg_crt_error_master_not_found">"Master key not found!"</string>
     <string name="msg_crt_error_nothing">"No keys certified!"</string>
     <string name="msg_crt_error_unlock">"Error unlocking master key!"</string>