diff --git a/src/apps/chifra/pkg/rpc/get_balance_cache_test.go b/src/apps/chifra/pkg/rpc/get_balance_cache_test.go
new file mode 100644
index 0000000000..856d4d8482
--- /dev/null
+++ b/src/apps/chifra/pkg/rpc/get_balance_cache_test.go
@@ -0,0 +1,120 @@
+package rpc
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/TrueBlocks/trueblocks-core/src/apps/chifra/pkg/base"
+)
+
+// TestGetBalanceAtCacheCollision tests that the in-memory balance cache
+// correctly distinguishes between different chains to prevent cache key collisions.
+// This test demonstrates the fix for issue #3993.
+func TestGetBalanceAtCacheCollision(t *testing.T) {
+	// Create two mock connections for different chains
+	conn1 := &Connection{
+		Chain:        "mainnet",
+		balanceCache: make(map[string]*base.Wei),
+	}
+
+	conn2 := &Connection{
+		Chain:        "gnosis",
+		balanceCache: make(map[string]*base.Wei),
+	}
+
+	// Test address and block number
+	testAddr := base.HexToAddress("0x1234567890123456789012345678901234567890")
+	testBlock := base.Blknum(1000000)
+
+	// Create different balance values for each chain
+	mainnetBalance := base.NewWei(1000)
+	gnosisBalance := base.NewWei(2000)
+
+	// Simulate caching balances for the same address/block on different chains
+	// With the fix, these should have different cache keys:
+	// - mainnet: "mainnet|0x1234567890123456789012345678901234567890|1000000"
+	// - gnosis:  "gnosis|0x1234567890123456789012345678901234567890|1000000"
+
+	// Store balance for mainnet
+	mainnetKey := fmt.Sprintf("%s|%s|%d", conn1.Chain, testAddr.Hex(), testBlock)
+	conn1.balanceCache[mainnetKey] = mainnetBalance
+
+	// Store balance for gnosis
+	gnosisKey := fmt.Sprintf("%s|%s|%d", conn2.Chain, testAddr.Hex(), testBlock)
+	conn2.balanceCache[gnosisKey] = gnosisBalance
+
+	// Verify that the cache keys are different
+	if mainnetKey == gnosisKey {
+		t.Errorf("Cache keys should be different for different chains, but both are: %s", mainnetKey)
+	}
+
+	// Verify we can retrieve the correct balance for each chain
+	if cachedMainnet, ok := conn1.balanceCache[mainnetKey]; !ok {
+		t.Error("Failed to retrieve mainnet balance from cache")
+	} else if cachedMainnet.String() != mainnetBalance.String() {
+		t.Errorf("Mainnet balance mismatch: got %s, want %s", cachedMainnet.String(), mainnetBalance.String())
+	}
+
+	if cachedGnosis, ok := conn2.balanceCache[gnosisKey]; !ok {
+		t.Error("Failed to retrieve gnosis balance from cache")
+	} else if cachedGnosis.String() != gnosisBalance.String() {
+		t.Errorf("Gnosis balance mismatch: got %s, want %s", cachedGnosis.String(), gnosisBalance.String())
+	}
+
+	// Test what would happen with the old cache key format (without chain)
+	// This demonstrates the bug that was fixed
+	oldKey := fmt.Sprintf("%s|%d", testAddr.Hex(), testBlock)
+
+	// If we used the old key format, one chain's balance would overwrite the other
+	oldCache := make(map[string]*base.Wei)
+	oldCache[oldKey] = mainnetBalance // mainnet writes first
+	oldCache[oldKey] = gnosisBalance  // gnosis overwrites it!
+
+	// With the old format, we'd get the wrong balance
+	if oldCache[oldKey].String() != gnosisBalance.String() {
+		t.Logf("Old cache format demonstration: mainnet balance was overwritten by gnosis balance")
+	}
+}
+
+// TestGetBalanceAtCacheKeyFormat verifies the exact format of cache keys
+func TestGetBalanceAtCacheKeyFormat(t *testing.T) {
+	tests := []struct {
+		name     string
+		chain    string
+		address  string
+		block    base.Blknum
+		expected string
+	}{
+		{
+			name:     "mainnet key",
+			chain:    "mainnet",
+			address:  "0x1234567890123456789012345678901234567890",
+			block:    1000000,
+			expected: "mainnet|0x1234567890123456789012345678901234567890|1000000",
+		},
+		{
+			name:     "gnosis key",
+			chain:    "gnosis",
+			address:  "0x1234567890123456789012345678901234567890",
+			block:    1000000,
+			expected: "gnosis|0x1234567890123456789012345678901234567890|1000000",
+		},
+		{
+			name:     "different block same address",
+			chain:    "mainnet",
+			address:  "0x1234567890123456789012345678901234567890",
+			block:    2000000,
+			expected: "mainnet|0x1234567890123456789012345678901234567890|2000000",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			addr := base.HexToAddress(tt.address)
+			key := fmt.Sprintf("%s|%s|%d", tt.chain, addr.Hex(), tt.block)
+			if key != tt.expected {
+				t.Errorf("Cache key format mismatch: got %s, want %s", key, tt.expected)
+			}
+		})
+	}
+}
diff --git a/src/apps/chifra/pkg/rpc/get_state.go b/src/apps/chifra/pkg/rpc/get_state.go
index eff794127e..b905f5ba59 100644
--- a/src/apps/chifra/pkg/rpc/get_state.go
+++ b/src/apps/chifra/pkg/rpc/get_state.go
@@ -150,7 +150,7 @@ func (conn *Connection) GetBalanceAt(addr base.Address, bn base.Blknum) (*base.W
 	var balance *base.Wei
 
 	// TODO: BOGUS - THIS IN MEMORY CACHE IS GOOD, BUT COULD BE BINARY FILE
-	key := fmt.Sprintf("%s|%d", addr.Hex(), bn)
+	key := fmt.Sprintf("%s|%s|%d", conn.Chain, addr.Hex(), bn)
 	conn.cacheMutex.Lock()
 	var ok bool
 	if balance, ok = conn.balanceCache[key]; ok {