diff --git a/src/runtime/mgcscavenge.go b/src/runtime/mgcscavenge.go
index 4c2fb4403c..db7c8121dc 100644
--- a/src/runtime/mgcscavenge.go
+++ b/src/runtime/mgcscavenge.go
@@ -602,9 +602,10 @@ func (m *pallocData) hasScavengeCandidate(min uintptr) bool {
 // findScavengeCandidate effectively returns entire free and unscavenged regions.
 // If max < pallocChunkPages, it may truncate the returned region such that size is
 // max. However, findScavengeCandidate may still return a larger region if, for
-// example, it chooses to preserve huge pages. That is, even if max is small,
-// size is not guaranteed to be equal to max. max is allowed to be less than min,
-// in which case it is as if max == min.
+// example, it chooses to preserve huge pages, or if max is not aligned to min (it
+// will round up). That is, even if max is small, the returned size is not guaranteed
+// to be equal to max. max is allowed to be less than min, in which case it is as if
+// max == min.
 func (m *pallocData) findScavengeCandidate(searchIdx uint, min, max uintptr) (uint, uint) {
 	if min&(min-1) != 0 || min == 0 {
 		print("runtime: min = ", min, "\n")
@@ -613,10 +614,15 @@ func (m *pallocData) findScavengeCandidate(searchIdx uint, min, max uintptr) (ui
 		print("runtime: min = ", min, "\n")
 		throw("min too large")
 	}
-	// max is allowed to be less than min, but we need to ensure
-	// we never truncate further than min.
-	if max < min {
+	// max may not be min-aligned, so we might accidentally truncate to
+	// a max value which causes us to return a non-min-aligned value.
+	// To prevent this, align max up to a multiple of min (which is always
+	// a power of 2). This also prevents max from ever being less than
+	// min, unless it's zero, so handle that explicitly.
+	if max == 0 {
 		max = min
+	} else {
+		max = alignUp(max, min)
 	}
 
 	i := int(searchIdx / 64)
diff --git a/src/runtime/mgcscavenge_test.go b/src/runtime/mgcscavenge_test.go
index ca507450db..b29a4d796a 100644
--- a/src/runtime/mgcscavenge_test.go
+++ b/src/runtime/mgcscavenge_test.go
@@ -184,6 +184,12 @@ func TestPallocDataFindScavengeCandidate(t *testing.T) {
 			max:       3 * m,
 			want:      BitRange{128, 3 * uint(m)},
 		}
+		tests["Max0"+suffix] = test{
+			scavenged: []BitRange{{0, PallocChunkPages - uint(m)}},
+			min:       m,
+			max:       0,
+			want:      BitRange{PallocChunkPages - uint(m), uint(m)},
+		}
 		if m <= 8 {
 			tests["OneFree"] = test{
 				alloc: []BitRange{{0, 40}, {40 + uint(m), PallocChunkPages - (40 + uint(m))}},
@@ -200,6 +206,12 @@ func TestPallocDataFindScavengeCandidate(t *testing.T) {
 			}
 		}
 		if m > 1 {
+			tests["MaxUnaligned"+suffix] = test{
+				scavenged: []BitRange{{0, PallocChunkPages - uint(m*2-1)}},
+				min:       m,
+				max:       m - 2,
+				want:      BitRange{PallocChunkPages - uint(m), uint(m)},
+			}
 			tests["SkipSmall"+suffix] = test{
 				alloc: []BitRange{{0, 64 - uint(m)}, {64, 5}, {70, 11}, {82, PallocChunkPages - 82}},
 				min:   m,