diff --git a/per-message-s3-exporter/firehose_reader.py b/per-message-s3-exporter/firehose_reader.py
index 990381b..9477cea 100644
--- a/per-message-s3-exporter/firehose_reader.py
+++ b/per-message-s3-exporter/firehose_reader.py
@@ -7,6 +7,7 @@
 import logging
 import os
 from pathlib import Path
+import re
 import ssl
 import time
 import warnings
@@ -15,6 +16,7 @@
 
 import attr
 
+EVENTS_RE: re.Pattern = re.compile(r"events\s+\"(?P<events>[a-z_ ]+)\"")
 FIREHOSE_MESSAGE_TYPES: List[str] = [
     "arrival",
     "cancellation",
@@ -62,7 +64,17 @@ def pitr_map_location() -> Path:
     return Path(os.getenv("PITR_MAP", "/home/firestarter/pitrs/.pitrs-map"))
 
 
-def pitr_map_from_file(init_time: str) -> Dict[str, int]:
+def pitr_map_message_types(init_args: str) -> List[str]:
+    """Return a list of all requested message types or all valid message types
+    if the initiation command does not specify a subset"""
+    events_match = EVENTS_RE.match(init_time)
+    if events_match is None:
+        return FIREHOSE_MESSAGE_TYPES
+
+    return events_match["events"]
+
+
+def pitr_map_from_file(init_time: str, init_args: str) -> Dict[str, int]:
     """Load PITR map from file, filling in a PITR value based on the init_time
     when appropriate
 
@@ -78,7 +90,8 @@ def pitr_map_from_file(init_time: str) -> Dict[str, int]:
         return {}
 
     start_pitr_from_env = int(init_time.split()[-1])
-    pitr_map = {message_type: start_pitr_from_env for message_type in FIREHOSE_MESSAGE_TYPES}
+    message_types = pitr_map_message_types(init_args)
+    pitr_map = {message_type: start_pitr_from_env for message_type in message_types}
 
     logging.info(f"Fetching start PITRs from {pitr_map_path}")
     with pitr_map_path.open(encoding="utf-8") as pitr_map_file:
@@ -117,13 +130,29 @@ def from_env(cls):
         init_time = os.environ.get("INIT_CMD_TIME", "live")
         init_time_split = init_time.split()
 
+        init_args = os.environ.get("INIT_CMD_ARGS", "")
+        for command in [
+            "live",
+            "pitr",
+            "range",
+            "compression",
+            "keepalive",
+            "username",
+            "password",
+        ]:
+            if command in init_args.split():
+                raise ValueError(
+                    f'$INIT_CMD_ARGS should not contain the "{command}" command. '
+                    "It belongs in its own variable."
+                )
+
         if init_time_split[0] not in ("live", "pitr", "range"):
             raise ValueError(
                 '$INIT_CMD_TIME value is invalid, should be "live", '
                 '"pitr <pitr>" or "range <start> <end>"'
             )
 
-        pitr_map = pitr_map_from_file(init_time)
+        pitr_map = pitr_map_from_file(init_time, init_args)
         if pitr_map:
             min_pitr = min(pitr_map.values())
             logging.info(f"Based on PITR map {pitr_map}")
@@ -135,22 +164,6 @@ def from_env(cls):
                 init_time_split[1] = f"{min_pitr}"
                 init_time = " ".join(init_time_split)
 
-        init_args = os.environ.get("INIT_CMD_ARGS", "")
-        for command in [
-            "live",
-            "pitr",
-            "range",
-            "compression",
-            "keepalive",
-            "username",
-            "password",
-        ]:
-            if command in init_args.split():
-                raise ValueError(
-                    f'$INIT_CMD_ARGS should not contain the "{command}" command. '
-                    "It belongs in its own variable."
-                )
-
         return cls(
             username=username,
             password=apikey,