diff --git a/src/cmd/compile/internal/types2/predicates.go b/src/cmd/compile/internal/types2/predicates.go
index 9cce189140..94a9b64761 100644
--- a/src/cmd/compile/internal/types2/predicates.go
+++ b/src/cmd/compile/internal/types2/predicates.go
@@ -6,10 +6,6 @@
 
 package types2
 
-import (
-	"sort"
-)
-
 // isNamed reports whether typ has a name.
 // isNamed may be called with types that are not fully set up.
 func isNamed(typ Type) bool {
@@ -329,8 +325,8 @@ func (check *Checker) identical0(x, y Type, cmpTags bool, p *ifacePair) bool {
 					p = p.prev
 				}
 				if debug {
-					assert(sort.IsSorted(byUniqueMethodName(a)))
-					assert(sort.IsSorted(byUniqueMethodName(b)))
+					assertSortedMethods(a)
+					assertSortedMethods(b)
 				}
 				for i, f := range a {
 					g := b[i]
diff --git a/src/cmd/compile/internal/types2/type.go b/src/cmd/compile/internal/types2/type.go
index 1bfde41159..22901b2ba9 100644
--- a/src/cmd/compile/internal/types2/type.go
+++ b/src/cmd/compile/internal/types2/type.go
@@ -8,7 +8,6 @@ package types2
 import (
 	"cmd/compile/internal/syntax"
 	"fmt"
-	"sort"
 )
 
 // A Type represents a type of Go.
@@ -481,8 +480,8 @@ func NewInterfaceType(methods []*Func, embeddeds []Type) *Interface {
 	}
 
 	// sort for API stability
-	sort.Sort(byUniqueMethodName(methods))
-	sort.Stable(byUniqueTypeName(embeddeds))
+	sortMethods(methods)
+	sortTypes(embeddeds)
 
 	typ.methods = methods
 	typ.embeddeds = embeddeds
@@ -685,7 +684,7 @@ func (t *Interface) Complete() *Interface {
 	}
 
 	if methods != nil {
-		sort.Sort(byUniqueMethodName(methods))
+		sortMethods(methods)
 		t.allMethods = methods
 	}
 	t.allTypes = allTypes
diff --git a/src/cmd/compile/internal/types2/typexpr.go b/src/cmd/compile/internal/types2/typexpr.go
index f0461d5895..d0bf229be9 100644
--- a/src/cmd/compile/internal/types2/typexpr.go
+++ b/src/cmd/compile/internal/types2/typexpr.go
@@ -876,8 +876,8 @@ func (check *Checker) interfaceType(ityp *Interface, iface *syntax.InterfaceType
 	}
 
 	// sort for API stability
-	sort.Sort(byUniqueMethodName(ityp.methods))
-	sort.Stable(byUniqueTypeName(ityp.embeddeds))
+	sortMethods(ityp.methods)
+	sortTypes(ityp.embeddeds)
 
 	check.later(func() { check.completeInterface(iface.Pos(), ityp) })
 }
@@ -985,7 +985,7 @@ func (check *Checker) completeInterface(pos syntax.Pos, ityp *Interface) {
 	}
 
 	if methods != nil {
-		sort.Sort(byUniqueMethodName(methods))
+		sortMethods(methods)
 		ityp.allMethods = methods
 	}
 	ityp.allTypes = allTypes
@@ -1029,6 +1029,10 @@ func intersect(x, y Type) (r Type) {
 	return NewSum(rtypes)
 }
 
+func sortTypes(list []Type) {
+	sort.Stable(byUniqueTypeName(list))
+}
+
 // byUniqueTypeName named type lists can be sorted by their unique type names.
 type byUniqueTypeName []Type
 
@@ -1043,6 +1047,19 @@ func sortName(t Type) string {
 	return ""
 }
 
+func sortMethods(list []*Func) {
+	sort.Sort(byUniqueMethodName(list))
+}
+
+func assertSortedMethods(list []*Func) {
+	if !debug {
+		panic("internal error: assertSortedMethods called outside debug mode")
+	}
+	if !sort.IsSorted(byUniqueMethodName(list)) {
+		panic("internal error: methods not sorted")
+	}
+}
+
 // byUniqueMethodName method lists can be sorted by their unique method names.
 type byUniqueMethodName []*Func
 
diff --git a/src/cmd/compile/internal/types2/unify.go b/src/cmd/compile/internal/types2/unify.go
index 60ccf625b9..ab19c5a38b 100644
--- a/src/cmd/compile/internal/types2/unify.go
+++ b/src/cmd/compile/internal/types2/unify.go
@@ -6,8 +6,6 @@
 
 package types2
 
-import "sort"
-
 // The unifier maintains two separate sets of type parameters x and y
 // which are used to resolve type parameters in the x and y arguments
 // provided to the unify call. For unidirectional unification, only
@@ -386,8 +384,8 @@ func (u *unifier) nify(x, y Type, p *ifacePair) bool {
 					p = p.prev
 				}
 				if debug {
-					assert(sort.IsSorted(byUniqueMethodName(a)))
-					assert(sort.IsSorted(byUniqueMethodName(b)))
+					assertSortedMethods(a)
+					assertSortedMethods(b)
 				}
 				for i, f := range a {
 					g := b[i]