diff --git a/include/llvm/ADT/PointerSumType.h b/include/llvm/ADT/PointerSumType.h
index 005b1c645c9..062544eedf8 100644
--- a/include/llvm/ADT/PointerSumType.h
+++ b/include/llvm/ADT/PointerSumType.h
@@ -94,7 +94,7 @@ public:
     return HelperT::template Lookup<N>::TraitsT::getFromVoidPointer(getImpl());
   }
 
-  operator bool() const { return Value & HelperT::PointerMask; }
+  explicit operator bool() const { return Value & HelperT::PointerMask; }
   bool operator==(const PointerSumType &R) const { return Value == R.Value; }
   bool operator!=(const PointerSumType &R) const { return Value != R.Value; }
   bool operator<(const PointerSumType &R) const { return Value < R.Value; }
diff --git a/include/llvm/Analysis/LazyCallGraph.h b/include/llvm/Analysis/LazyCallGraph.h
index 566e526f89b..bca0aebe2ee 100644
--- a/include/llvm/Analysis/LazyCallGraph.h
+++ b/include/llvm/Analysis/LazyCallGraph.h
@@ -148,7 +148,7 @@ public:
     ///
     /// This happens when an edge has been deleted. We leave the edge objects
     /// around but clear them.
-    operator bool() const;
+    explicit operator bool() const;
 
     /// Returnss the \c Kind of the edge.
     Kind getKind() const;
diff --git a/include/llvm/Support/CommandLine.h b/include/llvm/Support/CommandLine.h
index 204672f88dd..8d4ac81d294 100644
--- a/include/llvm/Support/CommandLine.h
+++ b/include/llvm/Support/CommandLine.h
@@ -201,7 +201,7 @@ public:
 
   void reset();
 
-  operator bool() const;
+  explicit operator bool() const;
 
   StringRef getName() const { return Name; }
   StringRef getDescription() const { return Description; }