diff --git a/.github/workflows/run-tests.yml b/.github/workflows/run-tests.yml
index aba68954..164bdd28 100644
--- a/.github/workflows/run-tests.yml
+++ b/.github/workflows/run-tests.yml
@@ -36,8 +36,8 @@ jobs:
         run: pytest
       - name: Validate poetry file
         run: poetry check
-      - name: Format files
-        run: black .
+      - name: Check source code format
+        run: black --check --diff .
 
   test-deb10-i386:
     runs-on: ubuntu-latest
diff --git a/wfdb/io/convert/edf.py b/wfdb/io/convert/edf.py
index 29e15ab2..8e1c59d9 100644
--- a/wfdb/io/convert/edf.py
+++ b/wfdb/io/convert/edf.py
@@ -189,7 +189,9 @@ def read_edf(
     ]
 
     # Number of bytes in header (8 bytes)
-    header_bytes = int(struct.unpack("<8s", edf_file.read(8))[0].decode(encoding))
+    header_bytes = int(
+        struct.unpack("<8s", edf_file.read(8))[0].decode(encoding)
+    )
     if verbose:
         print("Number of bytes in header record: {}".format(header_bytes))
 
@@ -222,7 +224,9 @@ def read_edf(
         )
 
     # Duration of a block, in seconds (8 bytes)
-    block_duration = float(struct.unpack("<8s", edf_file.read(8))[0].decode(encoding))
+    block_duration = float(
+        struct.unpack("<8s", edf_file.read(8))[0].decode(encoding)
+    )
     if verbose:
         print(
             "Duration of each data record in seconds: {}".format(block_duration)
@@ -240,7 +244,9 @@ def read_edf(
     # Label (e.g., EEG FpzCz or Body temp) (16 bytes each)
     sig_name = []
     for _ in range(n_sig):
-        temp_sig = struct.unpack("<16s", edf_file.read(16))[0].decode(encoding).strip()
+        temp_sig = (
+            struct.unpack("<16s", edf_file.read(16))[0].decode(encoding).strip()
+        )
         if temp_sig == "EDF Annotations" and not rdedfann_flag:
             print(
                 "*** This may be an EDF+ Annotation file instead, please see "
@@ -1118,7 +1124,9 @@ def rdedfann(
             adjusted_hex = hex(
                 struct.unpack("<H", struct.pack(">H", chunk + 1))[0]
             )
-            annotation_string += bytes.fromhex(adjusted_hex[2:]).decode(encoding)
+            annotation_string += bytes.fromhex(adjusted_hex[2:]).decode(
+                encoding
+            )
             # Remove all of the whitespace
             for rep in ["\x00", "\x14", "\x15"]:
                 annotation_string = annotation_string.replace(rep, " ")