diff --git a/lib/scanner/blocks.go b/lib/scanner/blocks.go
index dea7c0305..ec6d946c4 100644
--- a/lib/scanner/blocks.go
+++ b/lib/scanner/blocks.go
@@ -9,9 +9,9 @@ package scanner
 import (
 	"bytes"
 	"fmt"
-	"hash/adler32"
 	"io"
 
+	"github.com/chmduquesne/rollinghash/adler32"
 	"github.com/syncthing/syncthing/lib/protocol"
 	"github.com/syncthing/syncthing/lib/sha256"
 )
diff --git a/lib/scanner/blocks_test.go b/lib/scanner/blocks_test.go
index dc5c8d3c8..47d816a05 100644
--- a/lib/scanner/blocks_test.go
+++ b/lib/scanner/blocks_test.go
@@ -8,9 +8,13 @@ package scanner
 
 import (
 	"bytes"
+	"crypto/rand"
 	"fmt"
+	origAdler32 "hash/adler32"
 	"testing"
+	"testing/quick"
 
+	rollingAdler32 "github.com/chmduquesne/rollinghash/adler32"
 	"github.com/syncthing/syncthing/lib/protocol"
 )
 
@@ -160,3 +164,66 @@ func TestDiffEmpty(t *testing.T) {
 		}
 	}
 }
+
+func TestAdler32Variants(t *testing.T) {
+	// Verify that the two adler32 functions give matching results for a few
+	// different blocks of data.
+
+	hf1 := origAdler32.New()
+	hf2 := rollingAdler32.New()
+
+	checkFn := func(data []byte) bool {
+		hf1.Write(data)
+		sum1 := hf1.Sum32()
+
+		hf2.Write(data)
+		sum2 := hf2.Sum32()
+
+		hf1.Reset()
+		hf2.Reset()
+
+		return sum1 == sum2
+	}
+
+	// protocol block sized data
+	data := make([]byte, protocol.BlockSize)
+	for i := 0; i < 5; i++ {
+		rand.Read(data)
+		if !checkFn(data) {
+			t.Errorf("Hash mismatch on block sized data")
+		}
+	}
+
+	// random small blocks
+	if err := quick.Check(checkFn, nil); err != nil {
+		t.Error(err)
+	}
+
+	// rolling should have the same result as the individual blocks
+	// themselves. Which is not the same as the original non-rollind adler32
+	// blocks.
+
+	windowSize := 128
+
+	hf2.Reset()
+
+	hf3 := rollingAdler32.New()
+	hf3.Write(data[:windowSize])
+
+	for i := windowSize; i < len(data); i++ {
+		if i%windowSize == 0 {
+			// let the reference function catch up
+			hf2.Write(data[i-windowSize : i])
+
+			// verify that they are in sync with the rolling function
+			sum2 := hf2.Sum32()
+			sum3 := hf3.Sum32()
+			t.Logf("At i=%d, sum2=%08x, sum3=%08x", i, sum2, sum3)
+			if sum2 != sum3 {
+				t.Errorf("Mismatch after roll; i=%d, sum2=%08x, sum3=%08x", i, sum2, sum3)
+				break
+			}
+		}
+		hf3.Roll(data[i])
+	}
+}
diff --git a/vendor/github.com/chmduquesne/rollinghash/adler32/adler32.go b/vendor/github.com/chmduquesne/rollinghash/adler32/adler32.go
index a05df02d2..643a5987a 100644
--- a/vendor/github.com/chmduquesne/rollinghash/adler32/adler32.go
+++ b/vendor/github.com/chmduquesne/rollinghash/adler32/adler32.go
@@ -3,6 +3,7 @@
 package adler32
 
 import (
+	"hash"
 	vanilla "hash/adler32"
 
 	"github.com/chmduquesne/rollinghash"
@@ -22,6 +23,8 @@ type digest struct {
 	window []byte
 	oldest int
 	n      uint32
+
+	vanilla hash.Hash32
 }
 
 // Reset resets the Hash to its initial state.
@@ -37,7 +40,7 @@ func (d *digest) Reset() {
 // only used to determine which is the oldest element (leaving the
 // window). The calls to Roll() do not recompute the whole checksum.
 func New() rollinghash.Hash32 {
-	return &digest{a: 1, b: 0, window: nil, oldest: 0}
+	return &digest{a: 1, b: 0, window: nil, oldest: 0, vanilla: vanilla.New()}
 }
 
 // Size returns the number of bytes Sum will return.
@@ -53,13 +56,15 @@ func (d *digest) BlockSize() int { return 1 }
 // running hash. It never returns an error.
 func (d *digest) Write(p []byte) (int, error) {
 	// Copy the window
-	d.window = make([]byte, len(p))
+	if len(d.window) != len(p) {
+		d.window = make([]byte, len(p))
+	}
 	copy(d.window, p)
 
 	// Piggy-back on the core implementation
-	h := vanilla.New()
-	h.Write(p)
-	s := h.Sum32()
+	d.vanilla.Reset()
+	d.vanilla.Write(p)
+	s := d.vanilla.Sum32()
 	d.a, d.b = s&0xffff, s>>16
 	d.n = uint32(len(p)) % mod
 	return len(d.window), nil
diff --git a/vendor/manifest b/vendor/manifest
index e9947b4ef..7156200c9 100644
--- a/vendor/manifest
+++ b/vendor/manifest
@@ -46,10 +46,9 @@
 		},
 		{
 			"importpath": "github.com/chmduquesne/rollinghash",
-			"repository": "https://github.com/chmduquesne/rollinghash",
+			"repository": "https://github.com/kastelo/rollinghash",
 			"vcs": "git",
-			"revision": "88b86a92826991b14d01fb43456909fcb8a76b8b",
-			"branch": "master",
+			"branch": "reducealloc",
 			"notests": true
 		},
 		{
@@ -422,4 +421,4 @@
 			"notests": true
 		}
 	]
-}
\ No newline at end of file
+}