diff --git a/Borland/Threads.h b/Borland/Threads.h
index 337f4e2..2b95a75 100644
--- a/Borland/Threads.h
+++ b/Borland/Threads.h
@@ -97,7 +97,7 @@ namespace Loki
     template <class Host>
     class ObjectLevelLockable
     {
-        CRITICAL_SECTION mtx_;
+        mutable CRITICAL_SECTION mtx_;
 
     public:
         ObjectLevelLockable()
@@ -115,12 +115,12 @@ namespace Loki
         
         class Lock
         {
-            ObjectLevelLockable& host_;
+            ObjectLevelLockable const& host_;
 
             Lock(const Lock&);
             Lock& operator=(const Lock&);
         public:
-            Lock(Host& host) : host_(host)
+            Lock(const Host& host) : host_(host)
             {
                 ::EnterCriticalSection(&host_.mtx_);
             }
@@ -230,7 +230,7 @@ public:
                 }
                 ::EnterCriticalSection(&mtx_);
             }
-            Lock(Host&)
+            Lock(const Host&)
             {
                 if (!mtx_initialisation_done) {
                     initialize_impl();
diff --git a/MSVC/1300/Threads.h b/MSVC/1300/Threads.h
index 21508e9..ab6cd79 100644
--- a/MSVC/1300/Threads.h
+++ b/MSVC/1300/Threads.h
@@ -73,7 +73,7 @@ namespace Loki
     template <class Host>
     class ObjectLevelLockable
     {
-        CRITICAL_SECTION mtx_;
+        mutable CRITICAL_SECTION mtx_;
 
     public:
         ObjectLevelLockable()
@@ -91,13 +91,13 @@ namespace Loki
         
         class Lock
         {
-            ObjectLevelLockable& host_;
+            ObjectLevelLockable const& host_;
             
             Lock(const Lock&);
             Lock& operator=(const Lock&);
         public:
 
-            explicit Lock(ObjectLevelLockable& host) : host_(host)
+            explicit Lock(const ObjectLevelLockable& host) : host_(host)
             {
                 ::EnterCriticalSection(&host_.mtx_);
             }
@@ -157,7 +157,7 @@ namespace Loki
             {
                 ::EnterCriticalSection(&initializer_.mtx_);
             }
-            explicit Lock(ClassLevelLockable&)
+            explicit Lock(const ClassLevelLockable&)
             {
                 ::EnterCriticalSection(&initializer_.mtx_);
             }
diff --git a/Reference/Threads.h b/Reference/Threads.h
index 21508e9..ab6cd79 100644
--- a/Reference/Threads.h
+++ b/Reference/Threads.h
@@ -73,7 +73,7 @@ namespace Loki
     template <class Host>
     class ObjectLevelLockable
     {
-        CRITICAL_SECTION mtx_;
+        mutable CRITICAL_SECTION mtx_;
 
     public:
         ObjectLevelLockable()
@@ -91,13 +91,13 @@ namespace Loki
         
         class Lock
         {
-            ObjectLevelLockable& host_;
+            ObjectLevelLockable const& host_;
             
             Lock(const Lock&);
             Lock& operator=(const Lock&);
         public:
 
-            explicit Lock(ObjectLevelLockable& host) : host_(host)
+            explicit Lock(const ObjectLevelLockable& host) : host_(host)
             {
                 ::EnterCriticalSection(&host_.mtx_);
             }
@@ -157,7 +157,7 @@ namespace Loki
             {
                 ::EnterCriticalSection(&initializer_.mtx_);
             }
-            explicit Lock(ClassLevelLockable&)
+            explicit Lock(const ClassLevelLockable&)
             {
                 ::EnterCriticalSection(&initializer_.mtx_);
             }