diff --git a/cli/daemon/db.go b/cli/daemon/db.go
index a9b5a93ef2..f08ace9897 100644
--- a/cli/daemon/db.go
+++ b/cli/daemon/db.go
@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"net"
 	"strconv"
+	"strings"
 	"time"
 
 	"github.com/rs/zerolog/log"
@@ -50,6 +51,9 @@ func (s *Server) DBConnect(ctx context.Context, req *daemonpb.DBConnectRequest)
 	} else if appID == "" {
 		return nil, errNotLinked
 	}
+	if err := validateEnvName(ctx, appID, req.EnvName); err != nil {
+		return nil, err
+	}
 	port, passwd, err := sqldb.OneshotProxy(appID, req.EnvName, toRoleType(req.Role))
 	if err != nil {
 		return nil, err
@@ -176,6 +180,11 @@ func (s *Server) DBProxy(params *daemonpb.DBProxyRequest, stream daemonpb.Daemon
 	} else if appID == "" && params.EnvName != "local" {
 		return errNotLinked
 	}
+	if params.EnvName != "local" {
+		if err := validateEnvName(ctx, appID, params.EnvName); err != nil {
+			return err
+		}
+	}
 
 	ln, err := (&net.ListenConfig{}).Listen(ctx, "tcp", "127.0.0.1:"+strconv.Itoa(int(params.Port)))
 	if err != nil {
@@ -397,6 +406,35 @@ func serveProxy(ctx context.Context, ln net.Listener, handler func(context.Conte
 	}
 }
 
+// validateEnvName checks that the given environment slug exists for the app.
+// If not, it returns an error listing the available environment names.
+func validateEnvName(ctx context.Context, appSlug, envName string) error {
+	envs, err := platform.ListEnvs(ctx, appSlug)
+	if err != nil {
+		// If we can't list environments, skip validation and let the
+		// connection attempt proceed; it will fail with its own error.
+		return nil
+	}
+
+	for _, env := range envs {
+		if env.Slug == envName {
+			return nil
+		}
+	}
+
+	var slugs []string
+	for _, env := range envs {
+		slugs = append(slugs, env.Slug)
+	}
+	if len(slugs) > 0 {
+		return status.Errorf(codes.NotFound,
+			"environment %q not found; available environments for this app are: %s",
+			envName, strings.Join(slugs, ", "))
+	}
+	return status.Errorf(codes.NotFound,
+		"environment %q not found; this app has no environments", envName)
+}
+
 func getClusterType(req interface{ GetClusterType() daemonpb.DBClusterType }) sqldb.ClusterType {
 	switch req.GetClusterType() {
 	case daemonpb.DBClusterType_DB_CLUSTER_TYPE_RUN: