diff --git a/include/llvm/CodeGen/MachineOperand.h b/include/llvm/CodeGen/MachineOperand.h
index a782ff538ca..7fb2b9e7674 100644
--- a/include/llvm/CodeGen/MachineOperand.h
+++ b/include/llvm/CodeGen/MachineOperand.h
@@ -97,7 +97,7 @@ private:
     } OffsetedInfo;
   } Contents;
   
-  MachineOperand(MachineOperandType K) : OpKind(K), ParentMI(0) {}
+  explicit MachineOperand(MachineOperandType K) : OpKind(K), ParentMI(0) {}
 public:
   MachineOperand(const MachineOperand &M) {
     *this = M;
diff --git a/include/llvm/CodeGen/MachineRegisterInfo.h b/include/llvm/CodeGen/MachineRegisterInfo.h
index 47ffbfbab7c..2a62a83130c 100644
--- a/include/llvm/CodeGen/MachineRegisterInfo.h
+++ b/include/llvm/CodeGen/MachineRegisterInfo.h
@@ -54,7 +54,7 @@ class MachineRegisterInfo {
   MachineRegisterInfo(const MachineRegisterInfo&); // DO NOT IMPLEMENT
   void operator=(const MachineRegisterInfo&);      // DO NOT IMPLEMENT
 public:
-  MachineRegisterInfo(const MRegisterInfo &MRI);
+  explicit MachineRegisterInfo(const MRegisterInfo &MRI);
   ~MachineRegisterInfo();
   
   //===--------------------------------------------------------------------===//
@@ -203,7 +203,7 @@ public:
   class defusechain_iterator
     : public forward_iterator<MachineInstr, ptrdiff_t> {
     MachineOperand *Op;
-    defusechain_iterator(MachineOperand *op) : Op(op) {
+    explicit defusechain_iterator(MachineOperand *op) : Op(op) {
       // If the first node isn't one we're interested in, advance to one that
       // we are interested in.
       if (op) {
diff --git a/include/llvm/PassSupport.h b/include/llvm/PassSupport.h
index 9e86a724d6d..1ddc2df53da 100644
--- a/include/llvm/PassSupport.h
+++ b/include/llvm/PassSupport.h
@@ -144,7 +144,7 @@ struct RegisterPassBase {
     : PIObj(Name, Arg, TI, NormalCtor, CFGOnly) {
     registerPass();
   }
-  RegisterPassBase(intptr_t TI)
+  explicit RegisterPassBase(intptr_t TI)
     : PIObj("", "", TI) {
     // This ctor may only be used for analysis groups: it does not auto-register
     // the pass.
diff --git a/lib/VMCore/AsmWriter.cpp b/lib/VMCore/AsmWriter.cpp
index 310fa7f0065..94477bab252 100644
--- a/lib/VMCore/AsmWriter.cpp
+++ b/lib/VMCore/AsmWriter.cpp
@@ -57,10 +57,10 @@ public:
 /// @{
 public:
   /// @brief Construct from a module
-  SlotMachine(const Module *M);
+  explicit SlotMachine(const Module *M);
 
   /// @brief Construct from a function, starting out in incorp state.
-  SlotMachine(const Function *F);
+  explicit SlotMachine(const Function *F);
 
 /// @}
 /// @name Accessors