diff --git a/Source/OCMock/OCClassMockObject.h b/Source/OCMock/OCClassMockObject.h
index d654d810..1130cd15 100644
--- a/Source/OCMock/OCClassMockObject.h
+++ b/Source/OCMock/OCClassMockObject.h
@@ -23,4 +23,6 @@
 - (Class)mockedClass;
 - (Class)mockObjectClass;  // since -class returns the mockedClass
 
+- (void)scribbleOnMemory:(void *)start ofSize:(size_t)size;
+- (void)verifyScribbleAt:(void *)start ofSize:(size_t)size;
 @end
diff --git a/Source/OCMock/OCClassMockObject.m b/Source/OCMock/OCClassMockObject.m
index e2aa3680..acfe9c69 100644
--- a/Source/OCMock/OCClassMockObject.m
+++ b/Source/OCMock/OCClassMockObject.m
@@ -25,6 +25,8 @@ @interface OCClassMockObjectInstanceVars : NSObject
 @property (nonatomic) Class mockedClass;
 @property (nonatomic) Class originalMetaClass;
 @property (nonatomic) Class classCreatedForNewMetaClass;
+@property (nonatomic) void *classScribbleStart;
+@property (nonatomic) size_t classScribbleSize;
 @end
 
 @implementation OCClassMockObjectInstanceVars
@@ -34,24 +36,38 @@ @interface OCClassMockObject ()
 @property (nonatomic) Class mockedClass;
 @property (nonatomic) Class originalMetaClass;
 @property (nonatomic) Class classCreatedForNewMetaClass;
+@property (nonatomic) void *classScribbleStart;
+@property (nonatomic) size_t classScribbleSize;
 @end
 
 static const char *OCClassMockObjectInstanceVarsKey = "OCClassMockObjectInstanceVarsKey";
 
 @implementation OCClassMockObject
 
-#pragma mark  Initialisers, description, accessors, etc.
+#pragma mark  Initialisers, description, etc.
 
 - (id)initWithClass:(Class)aClass
 {
 	if(aClass == Nil)
 		[NSException raise:NSInvalidArgumentException format:@"Class cannot be Nil."];
 
+  size_t allocedSize = class_getInstanceSize(aClass);
+  Class selfClass = object_getClass(self);
+  size_t selfSize = class_getInstanceSize(selfClass);
+  if(allocedSize > selfSize)
+  {
+  	self = realloc(self, allocedSize);
+  }
 	self = [super init];
+
   OCClassMockObjectInstanceVars *vars = [[OCClassMockObjectInstanceVars alloc] init];
   objc_setAssociatedObject(self, OCClassMockObjectInstanceVarsKey, vars, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
   [vars release];
 
+  self.classScribbleSize = allocedSize - selfSize;
+  self.classScribbleStart = (void *)self + selfSize;
+  [self scribbleOnMemory:self.classScribbleStart ofSize:self.classScribbleSize];
+
 	self.mockedClass = aClass;
     [self prepareClassForClassMethodMocking];
 	return self;
@@ -68,9 +84,20 @@ - (NSString *)description
 	return [NSString stringWithFormat:@"OCClassMockObject(%@)", NSStringFromClass(self.mockedClass)];
 }
 
+- (void)scribbleOnMemory:(void *)start ofSize:(size_t)size
+{
+  bzero(start, size);
+}
+
+- (void)verifyScribbleAt:(void *)start ofSize:(size_t)size
+{
+  // Default version does no verification
+}
+
 #pragma mark  Setters/Getters
 
-- (OCClassMockObjectInstanceVars *)classMockObjectInstanceVars {
+- (OCClassMockObjectInstanceVars *)classMockObjectInstanceVars
+{
   return objc_getAssociatedObject(self, OCClassMockObjectInstanceVarsKey);
 }
 
@@ -89,6 +116,16 @@ - (Class)originalMetaClass
   return self.classMockObjectInstanceVars.originalMetaClass;
 }
 
+- (void *)classScribbleStart
+{
+  return self.classMockObjectInstanceVars.classScribbleStart;
+}
+
+- (size_t)classScribbleSize
+{
+  return self.classMockObjectInstanceVars.classScribbleSize;
+}
+
 - (void)setMockedClass:(Class)mockedClass
 {
   self.classMockObjectInstanceVars.mockedClass = mockedClass;
@@ -104,6 +141,15 @@ - (void)setOriginalMetaClass:(Class)originalMetaClass
   self.classMockObjectInstanceVars.originalMetaClass = originalMetaClass;
 }
 
+- (void)setClassScribbleSize:(size_t)classScribbleSize
+{
+  self.classMockObjectInstanceVars.classScribbleSize = classScribbleSize;
+}
+
+- (void)setClassScribbleStart:(void *)classScribbleStart
+{
+  self.classMockObjectInstanceVars.classScribbleStart = classScribbleStart;
+}
 
 #pragma mark  Extending/overriding superclass behaviour
 
@@ -119,6 +165,7 @@ - (void)stopMocking
         self.classCreatedForNewMetaClass = nil;
     }
     [super stopMocking];
+  	[self verifyScribbleAt:self.classScribbleStart ofSize:self.classScribbleSize];
 }
 
 
diff --git a/Source/OCMock/OCMockObject.m b/Source/OCMock/OCMockObject.m
index 95b1911e..bc6d03c1 100644
--- a/Source/OCMock/OCMockObject.m
+++ b/Source/OCMock/OCMockObject.m
@@ -106,7 +106,7 @@ + (id)observerMock
 }
 
 
-#pragma mark  Initialisers, description, accessors, etc.
+#pragma mark  Initialisers, description, etc.
 
 - (instancetype)init
 {
@@ -176,47 +176,61 @@ - (void)assertInvocationsArrayIsPresent
 }
 
 # pragma mark  Getters/Setters
-- (OCMockObjectInstanceVars *)mockObjectInstanceVars {
+- (OCMockObjectInstanceVars *)mockObjectInstanceVars
+{
   return objc_getAssociatedObject(self, OCMockObjectInstanceVarsKey);
 }
 
-- (BOOL)isNice {
+- (BOOL)isNice
+{
   return self.mockObjectInstanceVars.isNice;
 }
 
-- (BOOL)expectationOrderMatters {
+- (BOOL)expectationOrderMatters
+{
   return self.mockObjectInstanceVars.expectationOrderMatters;
 }
-- (NSMutableArray *)stubs {
+- (NSMutableArray *)stubs
+{
   return self.mockObjectInstanceVars.stubs;
 }
-- (NSMutableArray *)expectations {
+- (NSMutableArray *)expectations
+{
   return self.mockObjectInstanceVars.expectations;
 }
-- (NSMutableArray *)exceptions {
+- (NSMutableArray *)exceptions
+{
   return self.mockObjectInstanceVars.exceptions;
 }
-- (NSMutableArray *)invocations {
+
+- (NSMutableArray *)invocations
+{
   return self.mockObjectInstanceVars.invocations;
 }
 
-- (void)setIsNice:(BOOL)isNice {
+- (void)setIsNice:(BOOL)isNice
+{
   self.mockObjectInstanceVars.isNice = isNice;
 }
 
-- (void)setExpectationOrderMatters:(BOOL)expectationOrderMatters {
+- (void)setExpectationOrderMatters:(BOOL)expectationOrderMatters
+{
   self.mockObjectInstanceVars.expectationOrderMatters = expectationOrderMatters;
 }
-- (void)setStubs:(NSMutableArray *)stubs {
+- (void)setStubs:(NSMutableArray *)stubs
+{
   self.mockObjectInstanceVars.stubs = stubs;
 }
-- (void)setExpectations:(NSMutableArray *)expectations {
+- (void)setExpectations:(NSMutableArray *)expectations
+{
   self.mockObjectInstanceVars.expectations = expectations;
 }
-- (void)setExceptions:(NSMutableArray *)exceptions {
+- (void)setExceptions:(NSMutableArray *)exceptions
+{
   self.mockObjectInstanceVars.exceptions = exceptions;
 }
-- (void)setInvocations:(NSMutableArray *)invocations {
+- (void)setInvocations:(NSMutableArray *)invocations
+{
   self.mockObjectInstanceVars.invocations = invocations;
 }
 
diff --git a/Source/OCMock/OCPartialMockObject.m b/Source/OCMock/OCPartialMockObject.m
index c1f3d0f5..c6368a10 100644
--- a/Source/OCMock/OCPartialMockObject.m
+++ b/Source/OCMock/OCPartialMockObject.m
@@ -32,13 +32,18 @@ @implementation OCPartialMockObjectInstanceVars
 
 static const char *OCPartialMockObjectInstanceVarsKey = "OCPartialMockObjectInstanceVarsKey";
 
+// 0xEB chosen intentionally to try and force crashes.
+// It has both the high and low bit set, and 0xEBEBEBEBEB..etc
+// should be recognizable in a debugger as a bad value.
+static uint8_t OCScribbleByte = 0xEB;
+
 @interface OCPartialMockObject ()
 @property (nonatomic) NSObject *realObject;
 @end
 
 @implementation OCPartialMockObject
 
-#pragma mark  Initialisers, description, accessors, etc.
+#pragma mark  Initialisers, description, etc.
 
 - (id)initWithObject:(NSObject *)anObject
 {
@@ -61,9 +66,29 @@ - (NSString *)description
 	return [NSString stringWithFormat:@"OCPartialMockObject(%@)", NSStringFromClass(self.mockedClass)];
 }
 
+- (void)scribbleOnMemory:(void *)start ofSize:(size_t)size;
+{
+  for(size_t i = 0; i < size; ++i)
+  {
+    ((uint8_t*)start)[i] = OCScribbleByte;
+  }
+}
+
+- (void)verifyScribbleAt:(void *)start ofSize:(size_t)size;
+{
+  for(size_t i = 0; i < size; ++i)
+  {
+    if(((uint8_t*)start)[i] != OCScribbleByte)
+    {
+      [NSException raise:NSInternalInconsistencyException format:@"The class that partial mock `%@` does internal direct ivar accesses. You must use the real object instead of the mock for all uses other than setting/verifying stubs/expectations etc.", self];
+    }
+  }
+}
+
 #pragma mark  Setters/Getters
 
-- (OCPartialMockObjectInstanceVars *)partialMockObjectInstanceVars {
+- (OCPartialMockObjectInstanceVars *)partialMockObjectInstanceVars
+{
   return objc_getAssociatedObject(self, OCPartialMockObjectInstanceVarsKey);
 }
 
diff --git a/Source/OCMockTests/OCMockObjectTests.m b/Source/OCMockTests/OCMockObjectTests.m
index 081fd058..833ddffc 100644
--- a/Source/OCMockTests/OCMockObjectTests.m
+++ b/Source/OCMockTests/OCMockObjectTests.m
@@ -193,6 +193,22 @@ - (NSString *)stringValue;
 
 @end
 
+@interface TestClassLargeClass : NSObject
+{
+  int foo[4096];
+}
+@end
+
+@implementation TestClassLargeClass
+
+- (void)dirtyInstanceVariables:(TestClassLargeClass *)cls
+{
+  for(int i = 0; i < 4096; ++i) {
+    cls->foo[i] = i;
+  }
+}
+
+@end
 
 static NSString *TestNotification = @"TestNotification";
 
@@ -1108,6 +1124,28 @@ - (void)testMockObjectsHaveNoInstanceVariables
   XCTAssertEqual(class_getInstanceSize([NSProxy class]), class_getInstanceSize([OCClassMockObject class]));
 }
 
+- (void)testClassMockAllowsDirectMemoryAccess
+{
+  TestClassLargeClass *one = [[TestClassLargeClass alloc] init];
+  id mockOne = OCMClassMock([TestClassLargeClass class]);
+  [one dirtyInstanceVariables:mockOne];
+}
+
+- (void)performDirectMemoryAccess
+{
+  @autoreleasepool {
+    TestClassLargeClass *one = [[TestClassLargeClass alloc] init];
+    TestClassLargeClass *two = [[TestClassLargeClass alloc] init];
+    id mockTwo = OCMPartialMock(two);
+    [one dirtyInstanceVariables:mockTwo];
+  }
+}
+
+- (void)testPartialClassMockDoesNotAllowDirectMemoryAccess
+{
+  XCTAssertThrowsSpecificNamed([self performDirectMemoryAccess], NSException, NSInternalInconsistencyException);
+}
+
 @end