diff --git a/server/address_normalization_test.go b/server/address_normalization_test.go
new file mode 100644
index 0000000..a32184e
--- /dev/null
+++ b/server/address_normalization_test.go
@@ -0,0 +1,71 @@
+package server
+
+import (
+	"testing"
+)
+
+// TestNormalizeAddress verifies address normalization for case-insensitive comparison
+func TestNormalizeAddress(t *testing.T) {
+	tests := []struct {
+		name     string
+		addr1    string
+		addr2    string
+		expected bool // should they be equal after normalization?
+	}{
+		{
+			name:     "identical lowercase addresses",
+			addr1:    "0xeb5df7323c643f01b8c0643be808a0e6486621e8",
+			addr2:    "0xeb5df7323c643f01b8c0643be808a0e6486621e8",
+			expected: true,
+		},
+		{
+			name:     "identical uppercase addresses",
+			addr1:    "0XEB5DF7323C643F01B8C0643BE808A0E6486621E8",
+			addr2:    "0XEB5DF7323C643F01B8C0643BE808A0E6486621E8",
+			expected: true,
+		},
+		{
+			name:     "mixed case vs lowercase (EIP-55 checksum)",
+			addr1:    "0xeb5Df7323c643f01b8C0643bE808a0e6486621e8", // checksummed
+			addr2:    "0xeb5df7323c643f01b8c0643be808a0e6486621e8", // lowercase
+			expected: true,
+		},
+		{
+			name:     "mixed case vs uppercase",
+			addr1:    "0xeb5Df7323c643f01b8C0643bE808a0e6486621e8", // checksummed
+			addr2:    "0XEB5DF7323C643F01B8C0643BE808A0E6486621E8", // uppercase
+			expected: true,
+		},
+		{
+			name:     "different addresses (lowercase)",
+			addr1:    "0xeb5df7323c643f01b8c0643be808a0e6486621e8",
+			addr2:    "0x628f0be408bdf24451a1c30c452abbb9cfb50a18",
+			expected: false,
+		},
+		{
+			name:     "different addresses (mixed case)",
+			addr1:    "0xeb5Df7323c643f01b8C0643bE808a0e6486621e8",
+			addr2:    "0x628f0bE408bdf24451a1c30C452abbB9cfb50A18",
+			expected: false,
+		},
+		{
+			name:     "empty addresses",
+			addr1:    "",
+			addr2:    "",
+			expected: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			norm1 := normalizeAddress(tt.addr1)
+			norm2 := normalizeAddress(tt.addr2)
+			equal := norm1 == norm2
+
+			if equal != tt.expected {
+				t.Errorf("normalizeAddress(%q) vs normalizeAddress(%q):\ngot equal=%v, want equal=%v\nnorm1=%q, norm2=%q",
+					tt.addr1, tt.addr2, equal, tt.expected, norm1, norm2)
+			}
+		})
+	}
+}
diff --git a/server/handlers.go b/server/handlers.go
index 1dbaa9e..14ebfcc 100644
--- a/server/handlers.go
+++ b/server/handlers.go
@@ -10,6 +10,12 @@ import (
 	"time"
 )
 
+// normalizeAddress converts an Ethereum address to lowercase for case-insensitive comparison.
+// Ethereum addresses are case-insensitive; the mixed case (EIP-55 checksum) is optional validation.
+func normalizeAddress(addr string) string {
+	return strings.ToLower(addr)
+}
+
 // Handler manages HTTP requests for the mock server
 type Handler struct {
 	state  *State
@@ -546,7 +552,9 @@ func (h *Handler) handleOrderStatus(req InfoRequest) OrderQueryResult {
 		return OrderQueryResult{Status: "unknown_cloid"}
 	}
 
-	if order.Order.User != req.User {
+	// Compare normalized addresses for case-insensitive matching
+	// Ethereum addresses are case-insensitive; EIP-55 checksum is optional
+	if normalizeAddress(order.Order.User) != normalizeAddress(req.User) {
 		h.logger.Debug("order present but user does not match", slog.String("order.User", order.Order.User), slog.String("req.User", req.User))
 		return OrderQueryResult{Status: "unknown_cloid"}
 	}
diff --git a/server/websocket.go b/server/websocket.go
index 1f0af8d..12859d6 100644
--- a/server/websocket.go
+++ b/server/websocket.go
@@ -196,11 +196,13 @@ func (wsm *WebSocketManager) handleSubscribe(state *ConnectionState, sub map[str
 			wsm.sendError(state.conn, "Missing user address for orderUpdates")
 			return
 		}
+		// Normalize address for case-insensitive comparison
+		normalizedUser := normalizeAddress(user)
 		state.mu.Lock()
-		state.orderUpdatesUser = user
+		state.orderUpdatesUser = normalizedUser
 		state.mu.Unlock()
 
-		wsm.logger.Info("subscribed to orderUpdates", "user", user)
+		wsm.logger.Info("subscribed to orderUpdates", "user", user, "normalized", normalizedUser)
 
 		// Send subscription acknowledgment
 		wsm.sendSubscriptionResponse(state.conn, sub)
@@ -370,7 +372,8 @@ func (wsm *WebSocketManager) broadcastOrderUpdates() {
 				// Send if:
 				// 1. Order has no wallet (signature recovery failed) - backward compatibility
 				// 2. Order wallet matches subscriber wallet - proper isolation
-				if orderUser == "" || orderUser == subscribedUser {
+				//    (Compare normalized addresses for case-insensitive matching)
+				if orderUser == "" || normalizeAddress(orderUser) == subscribedUser {
 					shouldSend = true
 				}
 			}