diff --git a/builder/sizes_test.go b/builder/sizes_test.go
index 639c32b5c..0117065b6 100644
--- a/builder/sizes_test.go
+++ b/builder/sizes_test.go
@@ -42,9 +42,9 @@ 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", 4313, 323, 0, 2260},
-		{"microbit", "examples/serial", 2838, 382, 8, 2256},
-		{"wioterminal", "examples/pininterrupt", 8027, 1665, 132, 7488},
+		{"hifive1b", "examples/echo", 4321, 323, 0, 2268},
+		{"microbit", "examples/serial", 2842, 382, 8, 2264},
+		{"wioterminal", "examples/pininterrupt", 8039, 1665, 132, 7496},
 
 		// 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 78387cb31..3afed0a3e 100644
--- a/src/runtime/gc_blocks.go
+++ b/src/runtime/gc_blocks.go
@@ -56,6 +56,7 @@ var (
 	endBlock      gcBlock        // the block just past the end of the available space
 	gcTotalAlloc  uint64         // total number of bytes allocated
 	gcMallocs     uint64         // total number of allocations
+	gcNumGC       uint32         // total number of completed collection cycles
 	gcLock        task.PMutex    // lock to avoid race conditions on multicore systems
 )
 
@@ -610,6 +611,11 @@ func runGC() (freeBytes uintptr) {
 		dumpHeap()
 	}
 
+	// The cycle is complete. Counted here rather than in GC() so that
+	// collections triggered by an allocation are counted too. Every caller
+	// holds gcLock, the same lock ReadMemStats reads it under.
+	gcNumGC++
+
 	return
 }
 
@@ -850,6 +856,9 @@ func ReadMemStats(m *MemStats) {
 	// Record the total allocated bytes.
 	m.TotalAlloc = gcTotalAlloc
 
+	// Record the number of completed collection cycles.
+	m.NumGC = gcNumGC
+
 	gcLock.Unlock()
 }
 
diff --git a/src/runtime/gc_boehm.go b/src/runtime/gc_boehm.go
index e0fc16a67..66a78697f 100644
--- a/src/runtime/gc_boehm.go
+++ b/src/runtime/gc_boehm.go
@@ -129,6 +129,7 @@ func ReadMemStats(m *MemStats) {
 	m.Mallocs = 0 // not provided by bdwgc
 	m.Frees = 0   // not provided by bdwgc
 	m.Sys = uint64(gcMemStats.obtained_from_os_bytes)
+	m.NumGC = uint32(gcMemStats.gc_no)
 
 	gcLock.Unlock()
 }
diff --git a/src/runtime/gc_leaking.go b/src/runtime/gc_leaking.go
index 3f1595ff6..839acd8d9 100644
--- a/src/runtime/gc_leaking.go
+++ b/src/runtime/gc_leaking.go
@@ -109,6 +109,7 @@ func ReadMemStats(m *MemStats) {
 	m.HeapAlloc = gcTotalAlloc
 	m.HeapObjects = gcMallocs
 	m.Alloc = m.HeapAlloc
+	m.NumGC = 0 // this GC never collects, so no cycle ever completes
 
 	gcLock.Unlock()
 }
diff --git a/src/runtime/mstats.go b/src/runtime/mstats.go
index 987e17c30..4271bab9a 100644
--- a/src/runtime/mstats.go
+++ b/src/runtime/mstats.go
@@ -82,4 +82,9 @@ type MemStats struct {
 
 	// GCSys is bytes of memory in garbage collection metadata.
 	GCSys uint64
+
+	// NumGC is the number of completed GC cycles.
+	//
+	// The leaking collector never collects, so it always reports 0.
+	NumGC uint32
 }