diff --git a/libc/bionic/pthread_internal.cpp b/libc/bionic/pthread_internal.cpp
index 2b7a99a..c058384 100644
--- a/libc/bionic/pthread_internal.cpp
+++ b/libc/bionic/pthread_internal.cpp
@@ -43,7 +43,7 @@
 
 template <bool write> class ScopedRWLock {
  public:
-  ScopedRWLock(pthread_rwlock_t* rwlock) : rwlock_(rwlock) {
+  explicit ScopedRWLock(pthread_rwlock_t* rwlock) : rwlock_(rwlock) {
     (write ? pthread_rwlock_wrlock : pthread_rwlock_rdlock)(rwlock_);
   }
 
diff --git a/libc/malloc_debug/PointerData.h b/libc/malloc_debug/PointerData.h
index b05a763..6955c9a 100644
--- a/libc/malloc_debug/PointerData.h
+++ b/libc/malloc_debug/PointerData.h
@@ -112,7 +112,7 @@
 
 class PointerData : public OptionData {
  public:
-  PointerData(DebugData* debug_data);
+  explicit PointerData(DebugData* debug_data);
   virtual ~PointerData() = default;
 
   bool Initialize(const Config& config);
diff --git a/libc/private/ScopedReaddir.h b/libc/private/ScopedReaddir.h
index dc22309..9a20c09 100644
--- a/libc/private/ScopedReaddir.h
+++ b/libc/private/ScopedReaddir.h
@@ -22,10 +22,10 @@
 
 class ScopedReaddir {
  public:
-  ScopedReaddir(const char* path) : ScopedReaddir(opendir(path)) {
+  explicit ScopedReaddir(const char* path) : ScopedReaddir(opendir(path)) {
   }
 
-  ScopedReaddir(DIR* dir) {
+  explicit ScopedReaddir(DIR* dir) {
     dir_ = dir;
   }
 
diff --git a/libc/private/ScopedSignalHandler.h b/libc/private/ScopedSignalHandler.h
index dd5823f..7031752 100644
--- a/libc/private/ScopedSignalHandler.h
+++ b/libc/private/ScopedSignalHandler.h
@@ -33,7 +33,7 @@
     sigaction64(signal_number_, &action_, &old_action_);
   }
 
-  ScopedSignalHandler(int signal_number) : signal_number_(signal_number) {
+  explicit ScopedSignalHandler(int signal_number) : signal_number_(signal_number) {
     sigaction64(signal_number, nullptr, &old_action_);
   }
 
diff --git a/libc/private/bionic_lock.h b/libc/private/bionic_lock.h
index eebfeff..410e637 100644
--- a/libc/private/bionic_lock.h
+++ b/libc/private/bionic_lock.h
@@ -78,7 +78,7 @@
 
 class LockGuard {
  public:
-  LockGuard(Lock& lock) : lock_(lock) {
+  explicit LockGuard(Lock& lock) : lock_(lock) {
     lock_.lock();
   }
   ~LockGuard() {