diff --git a/include/avian/util/allocator.h b/include/avian/util/allocator.h
index 4b6d421b98..fc4163c775 100644
--- a/include/avian/util/allocator.h
+++ b/include/avian/util/allocator.h
@@ -18,10 +18,16 @@ namespace util {
 
 class Allocator {
  public:
-  // TODO: use size_t instead of unsigned
-  virtual void* tryAllocate(unsigned size) = 0;
-  virtual void* allocate(unsigned size) = 0;
-  virtual void free(const void* p, unsigned size) = 0;
+
+  // Returns null on failure
+  virtual void* tryAllocate(size_t size) = 0;
+
+  // Aborts on failure
+  virtual void* allocate(size_t size) = 0;
+
+  // By contract, size MUST be the original size of the allocated data, and p
+  // MUST point to the original base of the allocated data. No partial frees.
+  virtual void free(const void* p, size_t size) = 0;
 };
 
 }  // namespace util
diff --git a/include/avian/util/fixed-allocator.h b/include/avian/util/fixed-allocator.h
index 03fc61fcda..0d3898bcb1 100644
--- a/include/avian/util/fixed-allocator.h
+++ b/include/avian/util/fixed-allocator.h
@@ -24,13 +24,13 @@ class FixedAllocator : public Allocator {
  public:
   FixedAllocator(Aborter* a, Slice<uint8_t> memory);
 
-  virtual void* tryAllocate(unsigned size);
+  virtual void* tryAllocate(size_t size);
 
-  void* allocate(unsigned size, unsigned padAlignment);
+  void* allocate(size_t size, unsigned padAlignment);
 
-  virtual void* allocate(unsigned size);
+  virtual void* allocate(size_t size);
 
-  virtual void free(const void* p, unsigned size);
+  virtual void free(const void* p, size_t size);
 
   Aborter* a;
   Slice<uint8_t> memory;
diff --git a/src/avian/zone.h b/src/avian/zone.h
index 71e80aec90..fa1de3ddeb 100644
--- a/src/avian/zone.h
+++ b/src/avian/zone.h
@@ -95,7 +95,7 @@ class Zone : public avian::util::Allocator {
     }
   }
 
-  virtual void* tryAllocate(unsigned size)
+  virtual void* tryAllocate(size_t size)
   {
     size = pad(size);
     if (tryEnsure(size)) {
@@ -107,7 +107,7 @@ class Zone : public avian::util::Allocator {
     }
   }
 
-  virtual void* allocate(unsigned size)
+  virtual void* allocate(size_t size)
   {
     size = pad(size);
     void* p = tryAllocate(size);
@@ -146,7 +146,7 @@ class Zone : public avian::util::Allocator {
     segment = s;
   }
 
-  virtual void free(const void*, unsigned)
+  virtual void free(const void*, size_t)
   {
     // not supported
     abort(s);
diff --git a/src/heap/heap.cpp b/src/heap/heap.cpp
index 54ce4a4209..dfd6eb855a 100644
--- a/src/heap/heap.cpp
+++ b/src/heap/heap.cpp
@@ -60,10 +60,10 @@ class Context;
 
 Aborter* getAborter(Context* c);
 
-void* tryAllocate(Context* c, unsigned size);
-void* allocate(Context* c, unsigned size);
-void* allocate(Context* c, unsigned size, bool limit);
-void free(Context* c, const void* p, unsigned size);
+void* tryAllocate(Context* c, size_t size);
+void* allocate(Context* c, size_t size);
+void* allocate(Context* c, size_t size, bool limit);
+void free(Context* c, const void* p, size_t size);
 
 #ifdef USE_ATOMIC_OPERATIONS
 inline void markBitAtomic(uintptr_t* map, unsigned i)
@@ -1863,7 +1863,7 @@ void collect(Context* c)
   }
 }
 
-void* allocate(Context* c, unsigned size, bool limit)
+void* allocate(Context* c, size_t size, bool limit)
 {
   ACQUIRE(c->lock);
 
@@ -1888,12 +1888,12 @@ void* allocate(Context* c, unsigned size, bool limit)
   return 0;
 }
 
-void* tryAllocate(Context* c, unsigned size)
+void* tryAllocate(Context* c, size_t size)
 {
   return allocate(c, size, true);
 }
 
-void* allocate(Context* c, unsigned size)
+void* allocate(Context* c, size_t size)
 {
   void* p = allocate(c, size, false);
   expect(c->system, p);
@@ -1901,7 +1901,7 @@ void* allocate(Context* c, unsigned size)
   return p;
 }
 
-void free(Context* c, const void* p, unsigned size)
+void free(Context* c, const void* p, size_t size)
 {
   ACQUIRE(c->lock);
 
@@ -1925,7 +1925,7 @@ void free(Context* c, const void* p, unsigned size)
   c->count -= size;
 }
 
-void free_(Context* c, const void* p, unsigned size)
+void free_(Context* c, const void* p, size_t size)
 {
   free(c, p, size);
 }
@@ -1963,17 +1963,17 @@ class MyHeap : public Heap {
     return local::limitExceeded(&c, pendingAllocation);
   }
 
-  virtual void* tryAllocate(unsigned size)
+  virtual void* tryAllocate(size_t size)
   {
     return local::tryAllocate(&c, size);
   }
 
-  virtual void* allocate(unsigned size)
+  virtual void* allocate(size_t size)
   {
     return local::allocate(&c, size);
   }
 
-  virtual void free(const void* p, unsigned size)
+  virtual void free(const void* p, size_t size)
   {
     free_(&c, p, size);
   }
diff --git a/src/main.cpp b/src/main.cpp
index dad5a1a768..4471879ae8 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -68,12 +68,12 @@ const char* mainClass(const char* jar)
     {
     }
 
-    virtual void* tryAllocate(unsigned size)
+    virtual void* tryAllocate(size_t size)
     {
       return s->tryAllocate(size);
     }
 
-    virtual void* allocate(unsigned size)
+    virtual void* allocate(size_t size)
     {
       void* p = tryAllocate(size);
       if (p == 0) {
@@ -82,7 +82,7 @@ const char* mainClass(const char* jar)
       return p;
     }
 
-    virtual void free(const void* p, unsigned)
+    virtual void free(const void* p, size_t)
     {
       s->free(p);
     }
diff --git a/src/tools/type-generator/main.cpp b/src/tools/type-generator/main.cpp
index d983ebfded..b9bb30c84e 100644
--- a/src/tools/type-generator/main.cpp
+++ b/src/tools/type-generator/main.cpp
@@ -1636,12 +1636,12 @@ int main(int ac, char** av)
     {
     }
 
-    virtual void* tryAllocate(unsigned size)
+    virtual void* tryAllocate(size_t size)
     {
       return s->tryAllocate(size);
     }
 
-    virtual void* allocate(unsigned size)
+    virtual void* allocate(size_t size)
     {
       void* p = tryAllocate(size);
       if (p == 0) {
@@ -1650,7 +1650,7 @@ int main(int ac, char** av)
       return p;
     }
 
-    virtual void free(const void* p, unsigned)
+    virtual void free(const void* p, size_t)
     {
       s->free(p);
     }
diff --git a/src/util/fixed-allocator.cpp b/src/util/fixed-allocator.cpp
index 91d0d88621..bd250ce011 100644
--- a/src/util/fixed-allocator.cpp
+++ b/src/util/fixed-allocator.cpp
@@ -20,14 +20,14 @@ FixedAllocator::FixedAllocator(Aborter* a, Slice<uint8_t> memory)
 {
 }
 
-void* FixedAllocator::tryAllocate(unsigned size)
+void* FixedAllocator::tryAllocate(size_t size)
 {
   return allocate(size);
 }
 
-void* FixedAllocator::allocate(unsigned size, unsigned padAlignment)
+void* FixedAllocator::allocate(size_t size, unsigned padAlignment)
 {
-  unsigned paddedSize = vm::pad(size, padAlignment);
+  size_t paddedSize = vm::pad(size, padAlignment);
   expect(a, offset + paddedSize < memory.count);
 
   void* p = memory.begin() + offset;
@@ -35,12 +35,12 @@ void* FixedAllocator::allocate(unsigned size, unsigned padAlignment)
   return p;
 }
 
-void* FixedAllocator::allocate(unsigned size)
+void* FixedAllocator::allocate(size_t size)
 {
   return allocate(size, vm::BytesPerWord);
 }
 
-void FixedAllocator::free(const void* p, unsigned size)
+void FixedAllocator::free(const void* p, size_t size)
 {
   if (p >= memory.begin()
       and static_cast<const uint8_t*>(p) + size == memory.begin() + offset) {