diff --git a/linter-fast.json b/linter-fast.json
index fce445f2..3825fa61 100644
--- a/linter-fast.json
+++ b/linter-fast.json
@@ -11,6 +11,7 @@
         "gas",
         "misspell",
         "errcheck",
-        "vet"
+        "vet",
+        "goconst"
     ]
 }
diff --git a/linter.json b/linter.json
index 271a13cc..53308ba5 100644
--- a/linter.json
+++ b/linter.json
@@ -17,6 +17,7 @@
         "unparam",
         "errcheck",
         "vet",
-        "megacheck"
+        "megacheck",
+        "goconst"
     ]
 }
diff --git a/src/github.com/matrix-org/dendrite/mediaapi/thumbnailer/thumbnailer.go b/src/github.com/matrix-org/dendrite/mediaapi/thumbnailer/thumbnailer.go
index 6aa76cf0..83560373 100644
--- a/src/github.com/matrix-org/dendrite/mediaapi/thumbnailer/thumbnailer.go
+++ b/src/github.com/matrix-org/dendrite/mediaapi/thumbnailer/thumbnailer.go
@@ -63,22 +63,22 @@ func SelectThumbnail(desired types.ThumbnailSize, thumbnails []*types.ThumbnailM
 	bestFit := newThumbnailFitness()
 
 	for _, thumbnail := range thumbnails {
-		if desired.ResizeMethod == "scale" && thumbnail.ThumbnailSize.ResizeMethod != "scale" {
+		if desired.ResizeMethod == types.Scale && thumbnail.ThumbnailSize.ResizeMethod != types.Scale {
 			continue
 		}
 		fitness := calcThumbnailFitness(thumbnail.ThumbnailSize, thumbnail.MediaMetadata, desired)
-		if isBetter := fitness.betterThan(bestFit, desired.ResizeMethod == "crop"); isBetter {
+		if isBetter := fitness.betterThan(bestFit, desired.ResizeMethod == types.Crop); isBetter {
 			bestFit = fitness
 			chosenThumbnail = thumbnail
 		}
 	}
 
 	for _, thumbnailSize := range thumbnailSizes {
-		if desired.ResizeMethod == "scale" && thumbnailSize.ResizeMethod != "scale" {
+		if desired.ResizeMethod == types.Scale && thumbnailSize.ResizeMethod != types.Scale {
 			continue
 		}
 		fitness := calcThumbnailFitness(types.ThumbnailSize(thumbnailSize), nil, desired)
-		if isBetter := fitness.betterThan(bestFit, desired.ResizeMethod == "crop"); isBetter {
+		if isBetter := fitness.betterThan(bestFit, desired.ResizeMethod == types.Crop); isBetter {
 			bestFit = fitness
 			chosenThumbnailSize = (*types.ThumbnailSize)(&thumbnailSize)
 		}
diff --git a/src/github.com/matrix-org/dendrite/mediaapi/thumbnailer/thumbnailer_nfnt.go b/src/github.com/matrix-org/dendrite/mediaapi/thumbnailer/thumbnailer_nfnt.go
index a55a6d2a..caabf420 100644
--- a/src/github.com/matrix-org/dendrite/mediaapi/thumbnailer/thumbnailer_nfnt.go
+++ b/src/github.com/matrix-org/dendrite/mediaapi/thumbnailer/thumbnailer_nfnt.go
@@ -149,7 +149,7 @@ func createThumbnail(src types.Path, img image.Image, config types.ThumbnailSize
 	}
 
 	start := time.Now()
-	width, height, err := adjustSize(dst, img, config.Width, config.Height, config.ResizeMethod == "crop", logger)
+	width, height, err := adjustSize(dst, img, config.Width, config.Height, config.ResizeMethod == types.Crop, logger)
 	if err != nil {
 		return false, err
 	}
diff --git a/src/github.com/matrix-org/dendrite/mediaapi/types/types.go b/src/github.com/matrix-org/dendrite/mediaapi/types/types.go
index c7e5860d..855e8fe2 100644
--- a/src/github.com/matrix-org/dendrite/mediaapi/types/types.go
+++ b/src/github.com/matrix-org/dendrite/mediaapi/types/types.go
@@ -102,3 +102,9 @@ type ActiveThumbnailGeneration struct {
 	// The string key is a thumbnail file path
 	PathToResult map[string]*ThumbnailGenerationResult
 }
+
+// Crop indicates we should crop the thumbnail on resize
+const Crop = "crop"
+
+// Scale indicates we should scale the thumbnail on resize
+const Scale = "scale"
diff --git a/src/github.com/matrix-org/dendrite/mediaapi/writers/download.go b/src/github.com/matrix-org/dendrite/mediaapi/writers/download.go
index 901ab6d3..81907d55 100644
--- a/src/github.com/matrix-org/dendrite/mediaapi/writers/download.go
+++ b/src/github.com/matrix-org/dendrite/mediaapi/writers/download.go
@@ -179,9 +179,9 @@ func (r *downloadRequest) Validate() *util.JSONResponse {
 		}
 		// Default method to scale if not set
 		if r.ThumbnailSize.ResizeMethod == "" {
-			r.ThumbnailSize.ResizeMethod = "scale"
+			r.ThumbnailSize.ResizeMethod = types.Scale
 		}
-		if r.ThumbnailSize.ResizeMethod != "crop" && r.ThumbnailSize.ResizeMethod != "scale" {
+		if r.ThumbnailSize.ResizeMethod != types.Crop && r.ThumbnailSize.ResizeMethod != types.Scale {
 			return &util.JSONResponse{
 				Code: 400,
 				JSON: jsonerror.Unknown("method must be one of crop or scale"),
diff --git a/src/github.com/matrix-org/dendrite/roomserver/input/membership.go b/src/github.com/matrix-org/dendrite/roomserver/input/membership.go
index f4d8e02c..cd09001e 100644
--- a/src/github.com/matrix-org/dendrite/roomserver/input/membership.go
+++ b/src/github.com/matrix-org/dendrite/roomserver/input/membership.go
@@ -23,6 +23,13 @@ import (
 	"github.com/matrix-org/gomatrixserverlib"
 )
 
+// Membership values
+// TODO: Factor these out somewhere sensible?
+const join = "join"
+const leave = "leave"
+const invite = "invite"
+const ban = "ban"
+
 // updateMembership updates the current membership and the invites for each
 // user affected by a change in the current state of the room.
 // Returns a list of output events to write to the kafka log to inform the
@@ -83,9 +90,9 @@ func updateMembership(
 	updates []api.OutputEvent,
 ) ([]api.OutputEvent, error) {
 	var err error
-	// Default the membership to "leave" if no event was added or removed.
-	old := "leave"
-	new := "leave"
+	// Default the membership to Leave if no event was added or removed.
+	old := leave
+	new := leave
 
 	if remove != nil {
 		old, err = remove.Membership()
@@ -99,9 +106,9 @@ func updateMembership(
 			return nil, err
 		}
 	}
-	if old == new && new != "join" {
+	if old == new && new != join {
 		// If the membership is the same then nothing changed and we can return
-		// immediately, unless it's a "join" update (e.g. profile update).
+		// immediately, unless it's a Join update (e.g. profile update).
 		return updates, nil
 	}
 
@@ -111,11 +118,11 @@ func updateMembership(
 	}
 
 	switch new {
-	case "invite":
+	case invite:
 		return updateToInviteMembership(mu, add, updates)
-	case "join":
+	case join:
 		return updateToJoinMembership(mu, add, updates)
-	case "leave", "ban":
+	case leave, ban:
 		return updateToLeaveMembership(mu, add, new, updates)
 	default:
 		panic(fmt.Errorf(
@@ -176,7 +183,7 @@ func updateToJoinMembership(
 	for _, eventID := range retired {
 		orie := api.OutputRetireInviteEvent{
 			EventID:    eventID,
-			Membership: "join",
+			Membership: join,
 		}
 		if add != nil {
 			orie.RetiredByEventID = add.EventID()