diff --git a/builder/sizes_test.go b/builder/sizes_test.go
index 64cd4e77bf..628ddee896 100644
--- a/builder/sizes_test.go
+++ b/builder/sizes_test.go
@@ -41,9 +41,9 @@ func TestBinarySize(t *testing.T) {
 	// This is a small number of very diverse targets that we want to test.
 	tests := []sizeTest{
 		// microcontrollers
-		{"hifive1b", "examples/echo", 4484, 280, 0, 2252},
-		{"microbit", "examples/serial", 2808, 388, 8, 2256},
-		{"wioterminal", "examples/pininterrupt", 6064, 1484, 116, 6816},
+		{"hifive1b", "examples/echo", 4560, 280, 0, 2268},
+		{"microbit", "examples/serial", 2868, 388, 8, 2272},
+		{"wioterminal", "examples/pininterrupt", 6104, 1484, 116, 6832},
 
 		// TODO: also check wasm. Right now this is difficult, because
 		// wasm binaries are run through wasm-opt and therefore the
diff --git a/src/runtime/gc_blocks.go b/src/runtime/gc_blocks.go
index 7db6b7a1cf..1cc2384948 100644
--- a/src/runtime/gc_blocks.go
+++ b/src/runtime/gc_blocks.go
@@ -53,8 +53,10 @@ var (
 	nextAlloc     gcBlock        // the next block that should be tried by the allocator
 	endBlock      gcBlock        // the block just past the end of the available space
 	gcTotalAlloc  uint64         // total number of bytes allocated
+	gcTotalBlocks uint64         // total number of allocated blocks
 	gcMallocs     uint64         // total number of allocations
 	gcFrees       uint64         // total number of objects freed
+	gcFreedBlocks uint64         // total number of freed blocks
 )
 
 // zeroSizedAlloc is just a sentinel that gets returned when allocating 0 bytes.
@@ -285,6 +287,7 @@ func alloc(size uintptr, layout unsafe.Pointer) unsafe.Pointer {
 	gcMallocs++
 
 	neededBlocks := (size + (bytesPerBlock - 1)) / bytesPerBlock
+	gcTotalBlocks += uint64(neededBlocks)
 
 	// Continue looping until a run of free blocks has been found that fits the
 	// requested size.
@@ -619,6 +622,7 @@ func markRoot(addr, root uintptr) {
 // It returns how many bytes are free in the heap after the sweep.
 func sweep() (freeBytes uintptr) {
 	freeCurrentObject := false
+	var freed uint64
 	for block := gcBlock(0); block < endBlock; block++ {
 		switch block.state() {
 		case blockStateHead:
@@ -626,13 +630,13 @@ func sweep() (freeBytes uintptr) {
 			block.markFree()
 			freeCurrentObject = true
 			gcFrees++
-			freeBytes += bytesPerBlock
+			freed++
 		case blockStateTail:
 			if freeCurrentObject {
 				// This is a tail object following an unmarked head.
 				// Free it now.
 				block.markFree()
-				freeBytes += bytesPerBlock
+				freed++
 			}
 		case blockStateMark:
 			// This is a marked object. The next tail blocks must not be freed,
@@ -644,6 +648,8 @@ func sweep() (freeBytes uintptr) {
 			freeBytes += bytesPerBlock
 		}
 	}
+	gcFreedBlocks += freed
+	freeBytes += uintptr(freed) * bytesPerBlock
 	return
 }
 
@@ -690,6 +696,8 @@ func ReadMemStats(m *MemStats) {
 	m.Mallocs = gcMallocs
 	m.Frees = gcFrees
 	m.Sys = uint64(heapEnd - heapStart)
+	m.HeapAlloc = (gcTotalBlocks - gcFreedBlocks) * uint64(bytesPerBlock)
+	m.Alloc = m.HeapAlloc
 }
 
 func SetFinalizer(obj interface{}, finalizer interface{}) {
diff --git a/src/runtime/mstats.go b/src/runtime/mstats.go
index 2699e08b3f..7a6f8e637f 100644
--- a/src/runtime/mstats.go
+++ b/src/runtime/mstats.go
@@ -9,6 +9,11 @@ package runtime
 type MemStats struct {
 	// General statistics.
 
+	// Alloc is bytes of allocated heap objects.
+	//
+	// This is the same as HeapAlloc (see below).
+	Alloc uint64
+
 	// Sys is the total bytes of memory obtained from the OS.
 	//
 	// Sys is the sum of the XSys fields below. Sys measures the
@@ -18,6 +23,19 @@ type MemStats struct {
 
 	// Heap memory statistics.
 
+	// HeapAlloc is bytes of allocated heap objects.
+	//
+	// "Allocated" heap objects include all reachable objects, as
+	// well as unreachable objects that the garbage collector has
+	// not yet freed. Specifically, HeapAlloc increases as heap
+	// objects are allocated and decreases as the heap is swept
+	// and unreachable objects are freed. Sweeping occurs
+	// incrementally between GC cycles, so these two processes
+	// occur simultaneously, and as a result HeapAlloc tends to
+	// change smoothly (in contrast with the sawtooth that is
+	// typical of stop-the-world garbage collectors).
+	HeapAlloc uint64
+
 	// HeapSys is bytes of heap memory, total.
 	//
 	// In TinyGo unlike upstream Go, we make no distinction between