diff --git a/x/bank/keeper/keeper.go b/x/bank/keeper/keeper.go
index e94f50245ad6..9704e1595e8d 100644
--- a/x/bank/keeper/keeper.go
+++ b/x/bank/keeper/keeper.go
@@ -189,7 +189,7 @@ func (k BaseKeeper) GetSupply(ctx sdk.Context, denom string) sdk.Coin {
 	var amount sdk.Int
 	err := amount.Unmarshal(bz)
 	if err != nil {
-		panic("unexpected supply")
+		panic(fmt.Errorf("unable to unmarshal supply value %v", err))
 	}
 
 	return sdk.Coin{
diff --git a/x/bank/spec/01_state.md b/x/bank/spec/01_state.md
index 4b8a512489e6..5328e8b3caee 100644
--- a/x/bank/spec/01_state.md
+++ b/x/bank/spec/01_state.md
@@ -7,6 +7,6 @@ order: 1
 The `x/bank` module keeps state of three primary objects, account balances, denom metadata and the
 total supply of all balances.
 
-- Supply: `0x0 | byte(denom) -> ProtocolBuffer(coin)`
+- Supply: `0x0 | byte(denom) -> byte(amount)`
 - Denom Metadata: `0x1 | byte(denom) -> ProtocolBuffer(Metadata)`
 - Balances: `0x2 | byte(address length) | []byte(address) | []byte(balance.Denom) -> ProtocolBuffer(balance)`