diff --git a/lib/CodeGen/BranchFolding.cpp b/lib/CodeGen/BranchFolding.cpp
index 0fca9851794..055302f153a 100644
--- a/lib/CodeGen/BranchFolding.cpp
+++ b/lib/CodeGen/BranchFolding.cpp
@@ -46,7 +46,7 @@ namespace {
 
   struct BranchFolder : public MachineFunctionPass {
     static char ID;
-    BranchFolder(bool defaultEnableTailMerge) : 
+    explicit BranchFolder(bool defaultEnableTailMerge) : 
         MachineFunctionPass((intptr_t)&ID) {
           switch (FlagEnableTailMerge) {
           case cl::BOU_UNSET: EnableTailMerge = defaultEnableTailMerge; break;
diff --git a/lib/CodeGen/VirtRegMap.h b/lib/CodeGen/VirtRegMap.h
index b7cbe51cea3..e5d4b220fe0 100644
--- a/lib/CodeGen/VirtRegMap.h
+++ b/lib/CodeGen/VirtRegMap.h
@@ -75,7 +75,7 @@ namespace llvm {
     void operator=(const VirtRegMap&); // DO NOT IMPLEMENT
 
   public:
-    VirtRegMap(MachineFunction &mf);
+    explicit VirtRegMap(MachineFunction &mf);
 
     void grow();
 
diff --git a/lib/Target/ARM/ARMISelLowering.h b/lib/Target/ARM/ARMISelLowering.h
index 318657eb8e2..aba6ab3475a 100644
--- a/lib/Target/ARM/ARMISelLowering.h
+++ b/lib/Target/ARM/ARMISelLowering.h
@@ -76,7 +76,7 @@ namespace llvm {
   class ARMTargetLowering : public TargetLowering {
     int VarArgsFrameIndex;            // FrameIndex for start of varargs area.
   public:
-    ARMTargetLowering(TargetMachine &TM);
+    explicit ARMTargetLowering(TargetMachine &TM);
 
     virtual SDOperand LowerOperation(SDOperand Op, SelectionDAG &DAG);
     virtual const char *getTargetNodeName(unsigned Opcode) const;
diff --git a/lib/Target/Alpha/AlphaISelLowering.h b/lib/Target/Alpha/AlphaISelLowering.h
index 24e40a55764..291a56065d8 100644
--- a/lib/Target/Alpha/AlphaISelLowering.h
+++ b/lib/Target/Alpha/AlphaISelLowering.h
@@ -64,7 +64,7 @@ namespace llvm {
     int VarArgsBase;    // What is the base FrameIndex
     bool useITOF;
   public:
-    AlphaTargetLowering(TargetMachine &TM);
+    explicit AlphaTargetLowering(TargetMachine &TM);
     
     /// LowerOperation - Provide custom lowering hooks for some operations.
     ///
diff --git a/lib/Target/IA64/IA64ISelLowering.h b/lib/Target/IA64/IA64ISelLowering.h
index 6bc55348ce9..4a4e77186fb 100644
--- a/lib/Target/IA64/IA64ISelLowering.h
+++ b/lib/Target/IA64/IA64ISelLowering.h
@@ -43,7 +43,7 @@ namespace llvm {
     unsigned GP, SP, RP; // FIXME - clean this mess up
 	  
   public:
-    IA64TargetLowering(TargetMachine &TM);
+    explicit IA64TargetLowering(TargetMachine &TM);
 
     unsigned VirtGPR; // this is public so it can be accessed in the selector
                       // for ISD::RET. add an accessor instead? FIXME
diff --git a/lib/Target/Mips/MipsISelLowering.h b/lib/Target/Mips/MipsISelLowering.h
index 0199175a03f..4a62c94afeb 100644
--- a/lib/Target/Mips/MipsISelLowering.h
+++ b/lib/Target/Mips/MipsISelLowering.h
@@ -53,7 +53,7 @@ namespace llvm {
     // const MipsSubtarget &MipsSubTarget;
   public:
 
-    MipsTargetLowering(MipsTargetMachine &TM);
+    explicit MipsTargetLowering(MipsTargetMachine &TM);
 
     /// LowerOperation - Provide custom lowering hooks for some operations.
     virtual SDOperand LowerOperation(SDOperand Op, SelectionDAG &DAG);
diff --git a/lib/Target/PowerPC/PPCISelLowering.h b/lib/Target/PowerPC/PPCISelLowering.h
index 245fe53e5a7..b6b52ef31e1 100644
--- a/lib/Target/PowerPC/PPCISelLowering.h
+++ b/lib/Target/PowerPC/PPCISelLowering.h
@@ -186,7 +186,7 @@ namespace llvm {
     int ReturnAddrIndex;              // FrameIndex for return slot.
     const PPCSubtarget &PPCSubTarget;
   public:
-    PPCTargetLowering(PPCTargetMachine &TM);
+    explicit PPCTargetLowering(PPCTargetMachine &TM);
     
     /// getTargetNodeName() - This method returns the name of a target specific
     /// DAG node.
diff --git a/lib/Target/X86/X86ISelLowering.h b/lib/Target/X86/X86ISelLowering.h
index ef48095547e..55c34a3bbcb 100644
--- a/lib/Target/X86/X86ISelLowering.h
+++ b/lib/Target/X86/X86ISelLowering.h
@@ -286,7 +286,7 @@ namespace llvm {
     int BytesToPopOnReturn;           // Number of arg bytes ret should pop.
     int BytesCallerReserves;          // Number of arg bytes caller makes.
   public:
-    X86TargetLowering(TargetMachine &TM);
+    explicit X86TargetLowering(TargetMachine &TM);
 
     // Return the number of bytes that a function should pop when it returns (in
     // addition to the space used by the return address).