diff --git a/CHANGELOG.md b/CHANGELOG.md
index ff8c8861..9baf581f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -42,6 +42,8 @@
 
 - fix: rules/__init__.py: duplicate bytes_features line @williballenthin #3027
 
+- fix: EXTENSIONS_DYNAMIC has inconsistent leading dots @williballenthin #3028
+
 ### capa Explorer Web
 
 ### capa Explorer IDA Pro plugin
diff --git a/capa/helpers.py b/capa/helpers.py
index 45639da8..17dc2e13 100644
--- a/capa/helpers.py
+++ b/capa/helpers.py
@@ -58,16 +58,16 @@ from capa.features.common import (
     Format,
 )
 
-EXTENSIONS_SHELLCODE_32 = ("sc32", "raw32")
-EXTENSIONS_SHELLCODE_64 = ("sc64", "raw64")
+EXTENSIONS_SHELLCODE_32 = (".sc32", ".raw32")
+EXTENSIONS_SHELLCODE_64 = (".sc64", ".raw64")
 # CAPE (.json, .json_, .json.gz)
 # DRAKVUF (.log, .log.gz)
 # VMRay (.zip)
-EXTENSIONS_DYNAMIC = ("json", "json_", "json.gz", "log", ".log.gz", ".zip")
-EXTENSIONS_BINEXPORT2 = ("BinExport", "BinExport2")
-EXTENSIONS_ELF = "elf_"
-EXTENSIONS_FREEZE = "frz"
-EXTENSIONS_BINJA_DB = "bndb"
+EXTENSIONS_DYNAMIC = (".json", ".json_", ".json.gz", ".log", ".log.gz", ".zip")
+EXTENSIONS_BINEXPORT2 = (".BinExport", ".BinExport2")
+EXTENSIONS_ELF = ".elf_"
+EXTENSIONS_FREEZE = ".frz"
+EXTENSIONS_BINJA_DB = ".bndb"
 
 logger = logging.getLogger("capa")
 
@@ -197,7 +197,7 @@ def load_one_jsonl_from_path(jsonl_path: Path):
 
 
 def get_format_from_report(sample: Path) -> str:
-    if sample.name.endswith((".log", "log.gz")):
+    if sample.name.endswith((".log", ".log.gz")):
         line = load_one_jsonl_from_path(sample)
         if "Plugin" in line:
             return FORMAT_DRAKVUF
@@ -207,7 +207,7 @@ def get_format_from_report(sample: Path) -> str:
             if "logs/summary_v2.json" in namelist and "logs/flog.xml" in namelist:
                 # assume VMRay zipfile at a minimum has these files
                 return FORMAT_VMRAY
-    elif sample.name.endswith(("json", "json_", "json.gz")):
+    elif sample.name.endswith((".json", ".json_", ".json.gz")):
         report = load_json_from_path(sample)
         if "CAPE" in report:
             return FORMAT_CAPE
diff --git a/tests/test_helpers.py b/tests/test_helpers.py
index f40b2b37..26cb9d6c 100644
--- a/tests/test_helpers.py
+++ b/tests/test_helpers.py
@@ -20,6 +20,15 @@ from pathlib import Path
 import pytest
 
 import capa.helpers
+from capa.helpers import (
+    EXTENSIONS_ELF,
+    EXTENSIONS_FREEZE,
+    EXTENSIONS_DYNAMIC,
+    EXTENSIONS_BINJA_DB,
+    EXTENSIONS_BINEXPORT2,
+    EXTENSIONS_SHELLCODE_32,
+    EXTENSIONS_SHELLCODE_64,
+)
 from capa.features.extractors import helpers
 
 CD = Path(__file__).resolve().parent
@@ -106,3 +115,32 @@ def test_load_one_jsonl_from_path_empty_raises(tmp_path):
     p.write_bytes(b"")
     with pytest.raises(StopIteration):
         capa.helpers.load_one_jsonl_from_path(p)
+
+
+def test_extensions_dot_prefix():
+    for ext_group in (
+        EXTENSIONS_SHELLCODE_32,
+        EXTENSIONS_SHELLCODE_64,
+        EXTENSIONS_DYNAMIC,
+        EXTENSIONS_BINEXPORT2,
+        (EXTENSIONS_ELF,),
+        (EXTENSIONS_FREEZE,),
+        (EXTENSIONS_BINJA_DB,),
+    ):
+        for ext in ext_group:
+            assert ext.startswith("."), f"extension {ext!r} must start with a dot"
+
+    assert Path("sample.log").name.endswith(EXTENSIONS_DYNAMIC)
+    assert not Path("dialog").name.endswith(EXTENSIONS_DYNAMIC)
+    assert not Path("catalog").name.endswith(EXTENSIONS_DYNAMIC)
+    assert Path("report.json").name.endswith(EXTENSIONS_DYNAMIC)
+    assert not Path("notajson").name.endswith(EXTENSIONS_DYNAMIC)
+    assert Path("sample.sc32").name.endswith(EXTENSIONS_SHELLCODE_32)
+    assert Path("sample.raw32").name.endswith(EXTENSIONS_SHELLCODE_32)
+    assert Path("sample.sc64").name.endswith(EXTENSIONS_SHELLCODE_64)
+    assert Path("sample.raw64").name.endswith(EXTENSIONS_SHELLCODE_64)
+    assert Path("sample.BinExport").name.endswith(EXTENSIONS_BINEXPORT2)
+    assert Path("sample.BinExport2").name.endswith(EXTENSIONS_BINEXPORT2)
+    assert Path("sample.elf_").name.endswith(EXTENSIONS_ELF)
+    assert Path("sample.frz").name.endswith(EXTENSIONS_FREEZE)
+    assert Path("sample.bndb").name.endswith(EXTENSIONS_BINJA_DB)