diff --git a/internal/plugincommon/transmitters.go b/internal/plugincommon/transmitters.go
index 488fdd2cb..b7e8b66a4 100644
--- a/internal/plugincommon/transmitters.go
+++ b/internal/plugincommon/transmitters.go
@@ -2,6 +2,7 @@ package plugincommon
 
 import (
 	"fmt"
+	"sort"
 	"time"
 
 	"github.com/smartcontractkit/libocr/commontypes"
@@ -33,6 +34,9 @@ func GetTransmissionSchedule(
 		}
 	}
 
+	// transmissionSchedule must be deterministic
+	sort.Slice(transmitters, func(i, j int) bool { return transmitters[i] < transmitters[j] })
+
 	transmissionDelays := make([]time.Duration, len(transmitters))
 
 	for i := range transmissionDelays {
diff --git a/internal/plugincommon/transmitters_test.go b/internal/plugincommon/transmitters_test.go
index 01388304b..d7b21e293 100644
--- a/internal/plugincommon/transmitters_test.go
+++ b/internal/plugincommon/transmitters_test.go
@@ -50,6 +50,15 @@ func TestGetTransmissionSchedule(t *testing.T) {
 			expectedError:               true,
 			chainSupportReturnsError:    true,
 		},
+		{
+			name:                        "determinism check",
+			allTheOracles:               []commontypes.OracleID{3, 1, 2}, // <------ not ordered
+			oraclesSupportingDest:       []commontypes.OracleID{1, 3},
+			transmissionDelayMultiplier: 5 * time.Second,
+			expectedTransmitters:        []commontypes.OracleID{1, 3},
+			expectedTransmissionDelays:  []time.Duration{5 * time.Second, 10 * time.Second},
+			expectedError:               false,
+		},
 	}
 
 	for _, tc := range testCases {