diff --git a/keystore/auth_token_table.h b/keystore/auth_token_table.h
index a2f1446..bcf88fd 100644
--- a/keystore/auth_token_table.h
+++ b/keystore/auth_token_table.h
@@ -41,7 +41,7 @@
  */
 class AuthTokenTable {
   public:
-    AuthTokenTable(size_t max_entries = 32, time_t (*clock_function)() = clock_gettime_raw)
+    explicit AuthTokenTable(size_t max_entries = 32, time_t (*clock_function)() = clock_gettime_raw)
         : max_entries_(max_entries), clock_function_(clock_function) {}
 
     enum Error {
diff --git a/keystore/blob.h b/keystore/blob.h
index 584e312..3fa71ef 100644
--- a/keystore/blob.h
+++ b/keystore/blob.h
@@ -78,7 +78,7 @@
   public:
     Blob(const uint8_t* value, size_t valueLength, const uint8_t* info, uint8_t infoLength,
          BlobType type);
-    Blob(blob b);
+    explicit Blob(blob b);
 
     Blob();
 
diff --git a/keystore/key_store_service.h b/keystore/key_store_service.h
index 7d55919..64cbdd2 100644
--- a/keystore/key_store_service.h
+++ b/keystore/key_store_service.h
@@ -31,7 +31,7 @@
 
 class KeyStoreService : public BnKeystoreService, public IBinder::DeathRecipient {
   public:
-    KeyStoreService(KeyStore* keyStore) : mKeyStore(keyStore), mOperationMap(this) {}
+    explicit KeyStoreService(KeyStore* keyStore) : mKeyStore(keyStore), mOperationMap(this) {}
 
     void binderDied(const wp<IBinder>& who);
 
diff --git a/keystore/operation.h b/keystore/operation.h
index eb16257..083ec29 100644
--- a/keystore/operation.h
+++ b/keystore/operation.h
@@ -46,7 +46,7 @@
  */
 class OperationMap {
 public:
-    OperationMap(IBinder::DeathRecipient* deathRecipient);
+    explicit OperationMap(IBinder::DeathRecipient* deathRecipient);
     sp<IBinder> addOperation(keymaster_operation_handle_t handle, uint64_t keyid,
                              keymaster_purpose_t purpose, const keymaster2_device_t* dev,
                              sp<IBinder> appToken, keymaster_key_characteristics_t* characteristics,
diff --git a/keystore/user_state.h b/keystore/user_state.h
index 2a52f81..902719c 100644
--- a/keystore/user_state.h
+++ b/keystore/user_state.h
@@ -29,7 +29,7 @@
 
 class UserState {
   public:
-    UserState(uid_t userId);
+    explicit UserState(uid_t userId);
     ~UserState();
 
     bool initialize();