diff --git a/config.go b/config.go
index 50af7d9..9952b40 100644
--- a/config.go
+++ b/config.go
@@ -13,9 +13,9 @@ package config
 import (
 	"fmt"
 	"iter"
-	"maps"
 	"os"
 	"path/filepath"
+	"sort"
 	"strings"
 	"sync"
 
@@ -200,11 +200,26 @@ func (c *Config) Commit() error {
 	return nil
 }
 
-// All returns an iterator over all configuration values (including environment variables).
+// All returns an iterator over all configuration values in lexical key order
+// (including environment variables).
 func (c *Config) All() iter.Seq2[string, any] {
 	c.mu.RLock()
 	defer c.mu.RUnlock()
-	return maps.All(c.v.AllSettings())
+
+	settings := c.v.AllSettings()
+	keys := make([]string, 0, len(settings))
+	for key := range settings {
+		keys = append(keys, key)
+	}
+	sort.Strings(keys)
+
+	return func(yield func(string, any) bool) {
+		for _, key := range keys {
+			if !yield(key, settings[key]) {
+				return
+			}
+		}
+	}
 }
 
 // Path returns the path to the configuration file.
diff --git a/config_test.go b/config_test.go
index cfc376e..f53ff3e 100644
--- a/config_test.go
+++ b/config_test.go
@@ -90,6 +90,23 @@ func TestConfig_All_Good(t *testing.T) {
 	assert.Equal(t, "val2", all["key2"])
 }
 
+func TestConfig_All_Order_Good(t *testing.T) {
+	m := coreio.NewMockMedium()
+
+	cfg, err := New(WithMedium(m), WithPath("/tmp/test/config.yaml"))
+	assert.NoError(t, err)
+
+	_ = cfg.Set("zulu", "last")
+	_ = cfg.Set("alpha", "first")
+
+	var keys []string
+	for key, _ := range cfg.All() {
+		keys = append(keys, key)
+	}
+
+	assert.Equal(t, []string{"alpha", "zulu"}, keys)
+}
+
 func TestConfig_Path_Good(t *testing.T) {
 	m := coreio.NewMockMedium()
 
@@ -199,6 +216,21 @@ func TestLoadEnv_Good(t *testing.T) {
 	assert.Equal(t, "value", result["simple"])
 }
 
+func TestLoadEnv_PrefixNormalisation_Good(t *testing.T) {
+	t.Setenv("MYAPP_SETTING", "secret")
+	t.Setenv("MYAPP_ALPHA", "first")
+
+	keys := make([]string, 0, 2)
+	values := make([]string, 0, 2)
+	for key, value := range Env("MYAPP") {
+		keys = append(keys, key)
+		values = append(values, value.(string))
+	}
+
+	assert.Equal(t, []string{"alpha", "setting"}, keys)
+	assert.Equal(t, []string{"first", "secret"}, values)
+}
+
 func TestLoad_Bad(t *testing.T) {
 	m := coreio.NewMockMedium()
 
diff --git a/env.go b/env.go
index 64c0372..eff8519 100644
--- a/env.go
+++ b/env.go
@@ -3,17 +3,36 @@ package config
 import (
 	"iter"
 	"os"
+	"sort"
 	"strings"
 )
 
+func normaliseEnvPrefix(prefix string) string {
+	if prefix == "" || strings.HasSuffix(prefix, "_") {
+		return prefix
+	}
+	return prefix + "_"
+}
+
 // Env returns an iterator over environment variables with the given prefix,
 // providing them as dot-notation keys and values.
 //
+// The prefix may be supplied with or without a trailing underscore.
+//
 // For example, with prefix "CORE_CONFIG_":
 //
 //	CORE_CONFIG_FOO_BAR=baz  -> yields ("foo.bar", "baz")
 func Env(prefix string) iter.Seq2[string, any] {
 	return func(yield func(string, any) bool) {
+		prefix = normaliseEnvPrefix(prefix)
+
+		type entry struct {
+			key   string
+			value any
+		}
+
+		var entries []entry
+
 		for _, env := range os.Environ() {
 			if !strings.HasPrefix(env, prefix) {
 				continue
@@ -27,12 +46,19 @@ func Env(prefix string) iter.Seq2[string, any] {
 			name := parts[0]
 			value := parts[1]
 
-			// Strip prefix and convert to dot notation
 			key := strings.TrimPrefix(name, prefix)
 			key = strings.ToLower(key)
 			key = strings.ReplaceAll(key, "_", ".")
 
-			if !yield(key, value) {
+			entries = append(entries, entry{key: key, value: value})
+		}
+
+		sort.Slice(entries, func(i, j int) bool {
+			return entries[i].key < entries[j].key
+		})
+
+		for _, entry := range entries {
+			if !yield(entry.key, entry.value) {
 				return
 			}
 		}