diff --git a/src/runtime/mfixalloc.go b/src/runtime/mfixalloc.go
index 293c16b38b1..78ca861f65c 100644
--- a/src/runtime/mfixalloc.go
+++ b/src/runtime/mfixalloc.go
@@ -31,6 +31,7 @@ type fixalloc struct {
 	list   *mlink
 	chunk  uintptr // use uintptr instead of unsafe.Pointer to avoid write barriers
 	nchunk uint32
+	nalloc uint32
 	inuse  uintptr // in-use bytes now
 	stat   *sysMemStat
 	zero   bool // zero allocations
@@ -56,6 +57,7 @@ func (f *fixalloc) init(size uintptr, first func(arg, p unsafe.Pointer), arg uns
 	f.list = nil
 	f.chunk = 0
 	f.nchunk = 0
+	f.nalloc = uint32(_FixAllocChunk / f.size * f.size)
 	f.inuse = 0
 	f.stat = stat
 	f.zero = true
@@ -77,8 +79,8 @@ func (f *fixalloc) alloc() unsafe.Pointer {
 		return v
 	}
 	if uintptr(f.nchunk) < f.size {
-		f.chunk = uintptr(persistentalloc(_FixAllocChunk, 0, f.stat))
-		f.nchunk = _FixAllocChunk
+		f.chunk = uintptr(persistentalloc(uintptr(f.nalloc), 0, f.stat))
+		f.nchunk = f.nalloc
 	}
 
 	v := unsafe.Pointer(f.chunk)