diff --git a/src/runtime/mfixalloc.go b/src/runtime/mfixalloc.go
index 293c16b38b1..a81139a389c 100644
--- a/src/runtime/mfixalloc.go
+++ b/src/runtime/mfixalloc.go
@@ -50,6 +50,13 @@ type mlink struct {
 // Initialize f to allocate objects of the given size,
 // using the allocator to obtain chunks of memory.
 func (f *fixalloc) init(size uintptr, first func(arg, p unsafe.Pointer), arg unsafe.Pointer, stat *sysMemStat) {
+	if size > _FixAllocChunk {
+		throw("runtime: fixalloc size too large")
+	}
+	if min := unsafe.Sizeof(mlink{}); size < min {
+		size = min
+	}
+
 	f.size = size
 	f.first = first
 	f.arg = arg