diff --git a/echovault/api_string_test.go b/echovault/api_string_test.go
index 41e810a..2c21972 100644
--- a/echovault/api_string_test.go
+++ b/echovault/api_string_test.go
@@ -323,13 +323,27 @@ func TestEchoVault_APPEND(t *testing.T) {
 		wantErr     bool
 	}{
 		{
-			name:        "Return the correct string length for appended value",
+			name:    "Test APPEND with no preset value",
+			key:     "key1",
+			value:   "Hello ",
+			want:    6,
+			wantErr: false,
+		},
+		{
+			name:        "Test APPEND with preset value",
 			presetValue: "Hello ",
-			key:         "key1",
+			key:         "key2",
 			value:       "World",
 			want:        11,
 			wantErr:     false,
 		},
+		{
+			name:        "Test APPEND with integer preset value",
+			key:         "key3",
+			presetValue: 10,
+			value:       "Hello ",
+			wantErr:     true,
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
diff --git a/internal/modules/string/commands.go b/internal/modules/string/commands.go
index 1ab2550..a353f94 100644
--- a/internal/modules/string/commands.go
+++ b/internal/modules/string/commands.go
@@ -182,16 +182,19 @@ func handleAppend(params internal.HandlerFuncParams) ([]byte, error) {
 		}); err != nil {
 			return nil, err
 		}
-		return []byte(fmt.Sprintf("$%d\r\n%s\r\n", len(value), value)), nil
+		return []byte(fmt.Sprintf(":%d\r\n", len(value))), nil
+	}
+	currentValue, ok := params.GetValues(params.Context, []string{key})[key].(string)
+	if !ok {
+		return nil, fmt.Errorf("Value at key %s is not a string", key)
 	}
-	currentValue := params.GetValues(params.Context, []string{key})[key]
 	newValue := fmt.Sprintf("%v%s", currentValue, value)
 	if err = params.SetValues(params.Context, map[string]interface{}{
 		key: internal.AdaptType(newValue),
 	}); err != nil {
 		return nil, err
 	}
-	return []byte(fmt.Sprintf("$%d\r\n%s\r\n", len(newValue), newValue)), nil
+	return []byte(fmt.Sprintf(":%d\r\n", len(newValue))), nil
 }
 
 func Commands() []internal.Command {
diff --git a/internal/modules/string/commands_test.go b/internal/modules/string/commands_test.go
index c92e419..8b91ebf 100644
--- a/internal/modules/string/commands_test.go
+++ b/internal/modules/string/commands_test.go
@@ -16,14 +16,15 @@ package str_test
 
 import (
 	"errors"
+	"strconv"
+	"strings"
+	"testing"
+
 	"github.com/echovault/echovault/echovault"
 	"github.com/echovault/echovault/internal"
 	"github.com/echovault/echovault/internal/config"
 	"github.com/echovault/echovault/internal/constants"
 	"github.com/tidwall/resp"
-	"strconv"
-	"strings"
-	"testing"
 )
 
 func Test_String(t *testing.T) {
@@ -450,4 +451,106 @@ func Test_String(t *testing.T) {
 			})
 		}
 	})
+
+	t.Run("Test_HandleAppend", func(t *testing.T) {
+		t.Parallel()
+		conn, err := internal.GetConnection("localhost", port)
+		if err != nil {
+			t.Error(err)
+			return
+		}
+		defer func() {
+			_ = conn.Close()
+		}()
+		client := resp.NewConn(conn)
+
+		tests := []struct {
+			name             string
+			key              string
+			presetValue      interface{}
+			command          []string
+			expectedResponse int
+			expectedError    error
+		}{
+			{
+				name:             "Test APPEND with no preset value",
+				key:              "AppendKey1",
+				command:          []string{"APPEND", "AppendKey1", "Hello"},
+				expectedResponse: 5,
+				expectedError:    nil,
+			},
+			{
+				name:             "Test APPEND with preset value",
+				key:              "AppendKey2",
+				presetValue:      "Hello ",
+				command:          []string{"APPEND", "AppendKey2", "World"},
+				expectedResponse: 11,
+				expectedError:    nil,
+			},
+			{
+				name:             "Test APPEND with integer preset value",
+				key:              "AppendKey4",
+				presetValue:      10,
+				command:          []string{"APPEND", "AppendKey4", "World"},
+				expectedResponse: 0,
+				expectedError:    errors.New("Value at key AppendKey4 is not a string"),
+			},
+			{
+				name:          "Command too short",
+				command:       []string{"APPEND", "AppendKey5"},
+				expectedError: errors.New(constants.WrongArgsResponse),
+			},
+			{
+				name:          "Command too long",
+				command:       []string{"APPEND", "AppendKey5", "new value", "extra value"},
+				expectedError: errors.New(constants.WrongArgsResponse),
+			},
+		}
+
+		for _, test := range tests {
+			t.Run(test.name, func(t *testing.T) {
+				if test.presetValue != "" {
+					if err = client.WriteArray([]resp.Value{
+						resp.StringValue("SET"),
+						resp.StringValue(test.key),
+						resp.AnyValue(test.presetValue),
+					}); err != nil {
+						t.Error(err)
+					}
+					res, _, err := client.ReadValue()
+					if err != nil {
+						t.Error(err)
+					}
+
+					if !strings.EqualFold(res.String(), "ok") {
+						t.Errorf("expected preset response to be OK, got %s", res.String())
+					}
+				}
+
+				command := make([]resp.Value, len(test.command))
+				for i, c := range test.command {
+					command[i] = resp.StringValue(c)
+				}
+
+				if err = client.WriteArray(command); err != nil {
+					t.Error(err)
+				}
+				res, _, err := client.ReadValue()
+				if err != nil {
+					t.Error(err)
+				}
+
+				if test.expectedError != nil {
+					if !strings.Contains(res.Error().Error(), test.expectedError.Error()) {
+						t.Errorf("expected error \"%s\", got \"%s\"", test.expectedError.Error(), err.Error())
+					}
+					return
+				}
+
+				if res.Integer() != test.expectedResponse {
+					t.Errorf("expected response \"%d\", got \"%d\"", test.expectedResponse, res.Integer())
+				}
+			})
+		}
+	})
 }