diff --git a/src/runtime/mgc.go b/src/runtime/mgc.go
index aa7aa8bd0d..29bb8cde19 100644
--- a/src/runtime/mgc.go
+++ b/src/runtime/mgc.go
@@ -1025,6 +1025,13 @@ func gcStart(mode gcMode, forceTrigger bool) {
 		gcBgMarkPrepare() // Must happen before assist enable.
 		gcMarkRootPrepare()
 
+		// Mark all active tinyalloc blocks. Since we're
+		// allocating from these, they need to be black like
+		// other allocations. The alternative is to blacken
+		// the tiny block on every allocation from it, which
+		// would slow down the tiny allocator.
+		gcMarkTinyAllocs()
+
 		// At this point all Ps have enabled the write
 		// barrier, thus maintaining the no white to
 		// black invariant. Enable mutator assists to
diff --git a/src/runtime/mgcmark.go b/src/runtime/mgcmark.go
index edb8af25f5..13bbd071b1 100644
--- a/src/runtime/mgcmark.go
+++ b/src/runtime/mgcmark.go
@@ -1396,6 +1396,27 @@ func gcmarknewobject(obj, size, scanSize uintptr) {
 	}
 }
 
+// gcMarkTinyAllocs greys all active tiny alloc blocks.
+//
+// The world must be stopped.
+func gcMarkTinyAllocs() {
+	for _, p := range &allp {
+		if p == nil || p.status == _Pdead {
+			break
+		}
+		c := p.mcache
+		if c == nil || c.tiny == 0 {
+			continue
+		}
+		_, hbits, span, objIndex := heapBitsForObject(c.tiny, 0, 0)
+		gcw := &p.gcw
+		greyobject(c.tiny, 0, 0, hbits, span, gcw, objIndex)
+		if gcBlackenPromptly {
+			gcw.dispose()
+		}
+	}
+}
+
 // Checkmarking
 
 // To help debug the concurrent GC we remark with the world