diff --git a/src/main/java/com/google/devtools/build/lib/bazel/SpawnLogModule.java b/src/main/java/com/google/devtools/build/lib/bazel/SpawnLogModule.java
index aa2ba003f0b452..1d041efa251d6e 100644
--- a/src/main/java/com/google/devtools/build/lib/bazel/SpawnLogModule.java
+++ b/src/main/java/com/google/devtools/build/lib/bazel/SpawnLogModule.java
@@ -26,6 +26,7 @@
 import com.google.devtools.build.lib.remote.options.RemoteOptions;
 import com.google.devtools.build.lib.runtime.BlazeModule;
 import com.google.devtools.build.lib.runtime.CommandEnvironment;
+import com.google.devtools.build.lib.server.FailureDetails;
 import com.google.devtools.build.lib.server.FailureDetails.Execution;
 import com.google.devtools.build.lib.server.FailureDetails.Execution.Code;
 import com.google.devtools.build.lib.server.FailureDetails.FailureDetail;
@@ -87,6 +88,25 @@ private void initOutputs(CommandEnvironment env) throws IOException {
       return;
     }
 
+    if (executionOptions.executionLogBinaryFile != null
+        && executionOptions.executionLogJsonFile != null) {
+      String message =
+          "Must specify at most one of --execution_log_json_file and --execution_log_binary_file";
+      env.getBlazeModuleEnvironment()
+          .exit(
+              new AbruptExitException(
+                  DetailedExitCode.of(
+                      FailureDetail.newBuilder()
+                          .setMessage(message)
+                          .setExecutionOptions(
+                              FailureDetails.ExecutionOptions.newBuilder()
+                                  .setCode(
+                                      FailureDetails.ExecutionOptions.Code
+                                          .MULTIPLE_EXECUTION_LOG_FORMATS))
+                          .build())));
+      return;
+    }
+
     this.env = env;
 
     Path workingDirectory = env.getWorkingDirectory();
diff --git a/src/main/java/com/google/devtools/build/lib/exec/ExecutionOptions.java b/src/main/java/com/google/devtools/build/lib/exec/ExecutionOptions.java
index 5b688ba8cf8a17..96dddc660b2b95 100644
--- a/src/main/java/com/google/devtools/build/lib/exec/ExecutionOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/exec/ExecutionOptions.java
@@ -399,7 +399,7 @@ public boolean usingLocalTestJobs() {
       help =
           "Log the executed spawns into this file as delimited Spawn protos, according to"
               + " src/main/protobuf/spawn.proto. Related flags:"
-              + " --execution_log_json_file (text JSON format),"
+              + " --execution_log_json_file (text JSON format; mutually exclusive),"
               + " --execution_log_sort (whether to sort the execution log),"
               + " --subcommands (for displaying subcommands in terminal output).")
   public PathFragment executionLogBinaryFile;
@@ -414,7 +414,7 @@ public boolean usingLocalTestJobs() {
       help =
           "Log the executed spawns into this file as a JSON representation of the delimited Spawn"
               + " protos, according to src/main/protobuf/spawn.proto. Related flags:"
-              + " --execution_log_binary_file (binary protobuf format),"
+              + " --execution_log_binary_file (binary protobuf format; mutually exclusive),"
               + " --execution_log_sort (whether to sort the execution log),"
               + " --subcommands (for displaying subcommands in terminal output).")
   public PathFragment executionLogJsonFile;
diff --git a/src/main/protobuf/failure_details.proto b/src/main/protobuf/failure_details.proto
index e2f6ed867f7c07..ed165063702a7c 100644
--- a/src/main/protobuf/failure_details.proto
+++ b/src/main/protobuf/failure_details.proto
@@ -528,6 +528,7 @@ message ExecutionOptions {
         [(metadata) = { exit_code: 2 }];
     STRATEGY_NOT_FOUND = 9 [(metadata) = { exit_code: 2 }];
     DYNAMIC_STRATEGY_NOT_SANDBOXED = 10 [(metadata) = { exit_code: 2 }];
+    MULTIPLE_EXECUTION_LOG_FORMATS = 11 [(metadata) = { exit_code: 2 }];
 
     reserved 1, 2; // For internal use
   }