diff --git a/ethereum/statetransition/src/main/java/tech/pegasys/teku/statetransition/util/DebugDataDumper.java b/ethereum/statetransition/src/main/java/tech/pegasys/teku/statetransition/util/DebugDataDumper.java
index 6c0846cb414..a4bfad01fd8 100644
--- a/ethereum/statetransition/src/main/java/tech/pegasys/teku/statetransition/util/DebugDataDumper.java
+++ b/ethereum/statetransition/src/main/java/tech/pegasys/teku/statetransition/util/DebugDataDumper.java
@@ -164,14 +164,14 @@ String formatOptionalTimestamp(final Optional<UInt64> maybeTimestamp) {
 
   @VisibleForTesting
   String formatTimestamp(final UInt64 arrivalTimestamp) {
-    final DateFormat df = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SS");
+    final DateFormat df = new SimpleDateFormat("yyyy-MM-dd'T'HH_mm_ss.SS");
     final Date date = new Date(arrivalTimestamp.longValue());
     return df.format(date);
   }
 
   @VisibleForTesting
   String generateTimestamp(final TimeProvider timeProvider) {
-    final DateFormat df = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SS");
+    final DateFormat df = new SimpleDateFormat("yyyy-MM-dd'T'HH_mm_ss.SS");
     final Date date = new Date(timeProvider.getTimeInMillis().longValue());
     return df.format(date);
   }
diff --git a/ethereum/statetransition/src/test/java/tech/pegasys/teku/statetransition/util/DebugDataDumperTest.java b/ethereum/statetransition/src/test/java/tech/pegasys/teku/statetransition/util/DebugDataDumperTest.java
index 697711d3a73..e77dd7b26c8 100644
--- a/ethereum/statetransition/src/test/java/tech/pegasys/teku/statetransition/util/DebugDataDumperTest.java
+++ b/ethereum/statetransition/src/test/java/tech/pegasys/teku/statetransition/util/DebugDataDumperTest.java
@@ -165,20 +165,14 @@ void formatTimestamp_shouldFormatDate() {
     final DebugDataDumper manager = new DebugDataDumper(Path.of("."), true);
     final String formattedTimestamp =
         manager.formatOptionalTimestamp(Optional.of(timeProvider.getTimeInMillis()));
-
-    final DateFormat df = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SS");
-    final Date expectedDate = new Date(timeProvider.getTimeInMillis().longValue());
-    assertThat(formattedTimestamp).isEqualTo(df.format(expectedDate));
+    assertThat(formattedTimestamp).isEqualTo("1970-01-01T12_46_40.00");
   }
 
   @Test
   void generateTimestamp_shouldGenerateTimestamp() {
     final DebugDataDumper manager = new DebugDataDumper(Path.of("."), true);
     final String formattedTimestamp = manager.generateTimestamp(timeProvider);
-
-    final DateFormat df = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SS");
-    final Date expectedDate = new Date(timeProvider.getTimeInMillis().longValue());
-    assertThat(formattedTimestamp).isEqualTo(df.format(expectedDate));
+    assertThat(formattedTimestamp).isEqualTo("1970-01-01T12_46_40.00");
   }
 
   private void checkBytesSavedToFile(final Path path, final Bytes expectedBytes) {