diff --git a/baseapp/abci.go b/baseapp/abci.go
index 15646e438ab6..979089c5c86d 100644
--- a/baseapp/abci.go
+++ b/baseapp/abci.go
@@ -409,6 +409,14 @@ func (app *BaseApp) PrepareProposal(req *abci.PrepareProposalRequest) (resp *abc
 		return nil, errors.New("PrepareProposal handler not set")
 	}
 
+	// Abort any running OE so it cannot overlap with `PrepareProposal`. This could happen if optimistic
+	// `internalFinalizeBlock` from previous round takes a long time, but consensus has moved on to next round.
+	// Overlap is undesirable, since `internalFinalizeBlock` and `PrepareProoposal` could share access to
+	// in-memory structs depending on application implementation.
+	// No-op if OE is not enabled.
+	// Similar call to Abort() is done in `ProcessProposal`.
+	app.optimisticExec.Abort()
+
 	// Always reset state given that PrepareProposal can timeout and be called
 	// again in a subsequent round.
 	header := cmtproto.Header{