diff --git a/go/analysis/passes/bools/bools.go b/go/analysis/passes/bools/bools.go
index 833c9d7a..c82d3675 100644
--- a/go/analysis/passes/bools/bools.go
+++ b/go/analysis/passes/bools/bools.go
@@ -30,8 +30,13 @@ func run(pass *analysis.Pass) (interface{}, error) {
 	nodeFilter := []ast.Node{
 		(*ast.BinaryExpr)(nil),
 	}
+	seen := make(map[*ast.BinaryExpr]bool)
 	inspect.Preorder(nodeFilter, func(n ast.Node) {
 		e := n.(*ast.BinaryExpr)
+		if seen[e] {
+			// Already processed as a subexpression of an earlier node.
+			return
+		}
 
 		var op boolOp
 		switch e.Op {
@@ -43,10 +48,7 @@ func run(pass *analysis.Pass) (interface{}, error) {
 			return
 		}
 
-		// TODO(adonovan): this reports n(n-1)/2 errors for an
-		// expression e||...||e of depth n. Fix.
-		// See https://golang.org/issue/28086.
-		comm := op.commutativeSets(pass.TypesInfo, e)
+		comm := op.commutativeSets(pass.TypesInfo, e, seen)
 		for _, exprs := range comm {
 			op.checkRedundant(pass, exprs)
 			op.checkSuspect(pass, exprs)
@@ -70,8 +72,9 @@ var (
 // expressions in e that are connected by op.
 // For example, given 'a || b || f() || c || d' with the or op,
 // commutativeSets returns {{b, a}, {d, c}}.
-func (op boolOp) commutativeSets(info *types.Info, e *ast.BinaryExpr) [][]ast.Expr {
-	exprs := op.split(e)
+// commutativeSets adds any expanded BinaryExprs to seen.
+func (op boolOp) commutativeSets(info *types.Info, e *ast.BinaryExpr, seen map[*ast.BinaryExpr]bool) [][]ast.Expr {
+	exprs := op.split(e, seen)
 
 	// Partition the slice of expressions into commutative sets.
 	i := 0
@@ -188,11 +191,13 @@ func hasSideEffects(info *types.Info, e ast.Expr) bool {
 // split returns a slice of all subexpressions in e that are connected by op.
 // For example, given 'a || (b || c) || d' with the or op,
 // split returns []{d, c, b, a}.
-func (op boolOp) split(e ast.Expr) (exprs []ast.Expr) {
+// seen[e] is already true; any newly processed exprs are added to seen.
+func (op boolOp) split(e ast.Expr, seen map[*ast.BinaryExpr]bool) (exprs []ast.Expr) {
 	for {
 		e = unparen(e)
 		if b, ok := e.(*ast.BinaryExpr); ok && b.Op == op.tok {
-			exprs = append(exprs, op.split(b.Y)...)
+			seen[b] = true
+			exprs = append(exprs, op.split(b.Y, seen)...)
 			e = b.X
 		} else {
 			exprs = append(exprs, e)
diff --git a/go/analysis/passes/bools/testdata/src/a/a.go b/go/analysis/passes/bools/testdata/src/a/a.go
index c4b7dfdd..5358fbc0 100644
--- a/go/analysis/passes/bools/testdata/src/a/a.go
+++ b/go/analysis/passes/bools/testdata/src/a/a.go
@@ -46,22 +46,17 @@ func RatherStupidConditions() {
 	_ = i+1 == 1 || i+1 == 1         // want `redundant or: i\+1 == 1 \|\| i\+1 == 1`
 	_ = i == 1 || j+1 == i || i == 1 // want `redundant or: i == 1 \|\| i == 1`
 
-	// The various r.* patterns are intended to match duplicate
-	// diagnostics reported for the same underlying problem.
-	// See https://golang.org/issue/28086.
-	// TODO(adonovan): fix the checker.
-
-	_ = i == 1 || i == 1 || f() == 1 // want `redundant or: i == 1 \|\| i == 1` `r.*`
+	_ = i == 1 || i == 1 || f() == 1 // want `redundant or: i == 1 \|\| i == 1`
 	_ = i == 1 || f() == 1 || i == 1 // OK f may alter i as a side effect
 	_ = f() == 1 || i == 1 || i == 1 // want `redundant or: i == 1 \|\| i == 1`
 
 	// Test partition edge cases
-	_ = f() == 1 || i == 1 || i == 1 || j == 1 // want `redundant or: i == 1 \|\| i == 1` `r.*`
+	_ = f() == 1 || i == 1 || i == 1 || j == 1 // want `redundant or: i == 1 \|\| i == 1`
 	_ = f() == 1 || j == 1 || i == 1 || i == 1 // want `redundant or: i == 1 \|\| i == 1`
 	_ = i == 1 || f() == 1 || i == 1 || i == 1 // want `redundant or: i == 1 \|\| i == 1`
-	_ = i == 1 || i == 1 || f() == 1 || i == 1 // want `redundant or: i == 1 \|\| i == 1` `r.*` `r.*`
-	_ = i == 1 || i == 1 || j == 1 || f() == 1 // want `redundant or: i == 1 \|\| i == 1` `r.*` `r.*`
-	_ = j == 1 || i == 1 || i == 1 || f() == 1 // want `redundant or: i == 1 \|\| i == 1` `r.*`
+	_ = i == 1 || i == 1 || f() == 1 || i == 1 // want `redundant or: i == 1 \|\| i == 1`
+	_ = i == 1 || i == 1 || j == 1 || f() == 1 // want `redundant or: i == 1 \|\| i == 1`
+	_ = j == 1 || i == 1 || i == 1 || f() == 1 // want `redundant or: i == 1 \|\| i == 1`
 	_ = i == 1 || f() == 1 || f() == 1 || i == 1
 
 	_ = i == 1 || (i == 1 || i == 2)             // want `redundant or: i == 1 \|\| i == 1`
@@ -76,9 +71,9 @@ func RatherStupidConditions() {
 	_ = j == 0 ||
 		i == 1 ||
 		f() == 1 ||
-		j == 0 || // want `redundant or: j == 0 \|\| j == 0` `r.*`
-		i == 1 || // want `redundant or: i == 1 \|\| i == 1` `r.*` `r.*` `r.*`
-		i == 1 || // want `redundant or: i == 1 \|\| i == 1` `r.*` `r.*`
+		j == 0 || // want `redundant or: j == 0 \|\| j == 0`
+		i == 1 || // want `redundant or: i == 1 \|\| i == 1`
+		i == 1 || // want `redundant or: i == 1 \|\| i == 1`
 		i == 1 ||
 		j == 0 ||
 		k == 0
@@ -94,7 +89,7 @@ func RatherStupidConditions() {
 	_ = 0 != <-c && 0 != <-c         // OK subsequent receives may yield different values
 	_ = f() != 0 && f() != 0         // OK f might have side effects
 	_ = f != nil && f != nil         // want `redundant and: f != nil && f != nil`
-	_ = i != 1 && i != 1 && f() != 1 // want `redundant and: i != 1 && i != 1` `r.*`
+	_ = i != 1 && i != 1 && f() != 1 // want `redundant and: i != 1 && i != 1`
 	_ = i != 1 && f() != 1 && i != 1 // OK f may alter i as a side effect
 	_ = f() != 1 && i != 1 && i != 1 // want `redundant and: i != 1 && i != 1`
 }