diff --git a/base/check.cc b/base/check.cc
index 8c274fef..d69a6aa 100644
--- a/base/check.cc
+++ b/base/check.cc
@@ -9,17 +9,51 @@
 #include "base/check_op.h"
 #include "base/check_version_internal.h"
 #include "base/debug/alias.h"
+#include "base/debug/crash_logging.h"
 #include "base/debug/dump_without_crashing.h"
 #include "base/logging.h"
 #include "base/thread_annotations.h"
 #include "base/types/cxx23_to_underlying.h"
 #include "build/build_config.h"
-#include "base/debug/crash_logging.h"
 
 namespace logging {
 
 namespace {
 
+// End check failure messages with a period, e.g.:
+//
+//   CHECK(false);
+//
+// Yields:
+//
+//   Check failed: false.
+//
+// Or, with additional data streamed in:
+//
+//   CHECK(false) << "foo";
+//
+// The output is:
+//
+//   Check failed: false. foo
+//
+// In fuzzing mode, however, in a bid to help machines understand where to draw
+// the line between the compile-time static part ("false") and the
+// runtime-variable part ("foo"), we use a semicolon instead. It seems quite
+// difficult to manage to embed a semilicon in the compile-time static part.
+// Thus the examples above become:
+//
+//   Check failed: false;
+//   Check failed: false; foo
+//
+// See crbug.com/443588668 for more details.
+constexpr char kCheckFailureMessageSeparator[] =
+#ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
+    "; "
+#else
+    ". "
+#endif
+    ;
+
 LogSeverity GetDumpSeverity() {
 #if defined(OFFICIAL_BUILD)
   return DCHECK_IS_ON() ? LOGGING_DCHECK : LOGGING_ERROR;
@@ -217,7 +251,8 @@
   auto* const log_message = new CheckLogMessage(
       location, GetCheckSeverity(fatal_milestone), fatal_milestone);
   // TODO(pbos): Make this output CHECK instead of Check.
-  log_message->stream() << "Check failed: " << condition << ". ";
+  log_message->stream() << "Check failed: " << condition
+                        << kCheckFailureMessageSeparator;
   return CheckError(log_message);
 }
 
@@ -227,7 +262,8 @@
   auto* const log_message = new CheckLogMessage(
       location, GetCheckSeverity(fatal_milestone), fatal_milestone);
   // TODO(pbos): Make this output CHECK instead of Check.
-  log_message->stream() << "Check failed: " << log_message_str;
+  log_message->stream() << "Check failed: " << log_message_str
+                        << kCheckFailureMessageSeparator;
   free(log_message_str);
   return log_message;
 }
@@ -235,14 +271,16 @@
 CheckError CheckError::DCheck(const char* condition,
                               const base::Location& location) {
   auto* const log_message = new DCheckLogMessage(location);
-  log_message->stream() << "DCHECK failed: " << condition << ". ";
+  log_message->stream() << "DCHECK failed: " << condition
+                        << kCheckFailureMessageSeparator;
   return CheckError(log_message);
 }
 
 LogMessage* CheckError::DCheckOp(char* log_message_str,
                                  const base::Location& location) {
   auto* const log_message = new DCheckLogMessage(location);
-  log_message->stream() << "DCHECK failed: " << log_message_str;
+  log_message->stream() << "DCHECK failed: " << log_message_str
+                        << kCheckFailureMessageSeparator;
   free(log_message_str);
   return log_message;
 }
@@ -253,7 +291,8 @@
       new CheckLogMessage(location, GetDumpSeverity(),
                           base::NotFatalUntil::NoSpecifiedMilestoneInternal);
   // TODO(pbos): Make this output CHECK instead of Check.
-  log_message->stream() << "Check failed: " << condition << ". ";
+  log_message->stream() << "Check failed: " << condition
+                        << kCheckFailureMessageSeparator;
   return CheckError(log_message);
 }
 
@@ -263,7 +302,8 @@
       new CheckLogMessage(location, GetDumpSeverity(),
                           base::NotFatalUntil::NoSpecifiedMilestoneInternal);
   // TODO(pbos): Make this output CHECK instead of Check.
-  log_message->stream() << "Check failed: " << log_message_str;
+  log_message->stream() << "Check failed: " << log_message_str
+                        << kCheckFailureMessageSeparator;
   free(log_message_str);
   return log_message;
 }
@@ -276,7 +316,8 @@
 #elif BUILDFLAG(IS_POSIX) || BUILDFLAG(IS_FUCHSIA)
   auto* const log_message = new DCheckErrnoLogMessage(location, err_code);
 #endif
-  log_message->stream() << "DCHECK failed: " << condition << ". ";
+  log_message->stream() << "DCHECK failed: " << condition
+                        << kCheckFailureMessageSeparator;
   return CheckError(log_message);
 }
 
@@ -285,7 +326,8 @@
   auto* const log_message = new LogMessage(
       location.file_name(), location.line_number(), LOGGING_ERROR);
   // TODO(pbos): Make this output NOTIMPLEMENTED instead of Not implemented.
-  log_message->stream() << "Not implemented reached in " << function;
+  log_message->stream() << "Not implemented reached in " << function
+                        << kCheckFailureMessageSeparator;
   return CheckError(log_message);
 }
 
@@ -332,7 +374,8 @@
       new CheckLogMessage(location, LOGGING_FATAL,
                           base::NotFatalUntil::NoSpecifiedMilestoneInternal);
   // TODO(pbos): Make this output CHECK instead of Check.
-  log_message->stream() << "Check failed: " << condition << ". ";
+  log_message->stream() << "Check failed: " << condition
+                        << kCheckFailureMessageSeparator;
   return CheckNoreturnError(log_message);
 }
 
@@ -342,7 +385,8 @@
       new CheckLogMessage(location, LOGGING_FATAL,
                           base::NotFatalUntil::NoSpecifiedMilestoneInternal);
   // TODO(pbos): Make this output CHECK instead of Check.
-  log_message->stream() << "Check failed: " << log_message_str;
+  log_message->stream() << "Check failed: " << log_message_str
+                        << kCheckFailureMessageSeparator;
   free(log_message_str);
   return log_message;
 }
@@ -358,7 +402,8 @@
       location.file_name(), location.line_number(), LOGGING_FATAL, err_code);
 #endif
   // TODO(pbos): Make this output CHECK instead of Check.
-  log_message->stream() << "Check failed: " << condition << ". ";
+  log_message->stream() << "Check failed: " << condition
+                        << kCheckFailureMessageSeparator;
   return CheckNoreturnError(log_message);
 }
 
diff --git a/base/check_unittest.cc b/base/check_unittest.cc
index ae5e0d0..06ca33e 100644
--- a/base/check_unittest.cc
+++ b/base/check_unittest.cc
@@ -177,9 +177,9 @@
   EXPECT_CHECK("Check failed: false. foo", CHECK(false) << "foo");
 
   double a = 2, b = 1;
-  EXPECT_CHECK("Check failed: a < b (2.000000 vs. 1.000000)", CHECK_LT(a, b));
+  EXPECT_CHECK("Check failed: a < b (2.000000 vs. 1.000000). ", CHECK_LT(a, b));
 
-  EXPECT_CHECK("Check failed: a < b (2.000000 vs. 1.000000)custom message",
+  EXPECT_CHECK("Check failed: a < b (2.000000 vs. 1.000000). custom message",
                CHECK_LT(a, b) << "custom message");
 }
 
@@ -189,29 +189,17 @@
   std::string err =
       logging::SystemErrorCodeToString(logging::GetLastSystemErrorCode());
 
-  EXPECT_CHECK(
-      "Check failed: fopen(file, \"r\") != nullptr."
-      " : " +
-          err,
-      PCHECK(fopen(file, "r") != nullptr));
+  EXPECT_CHECK("Check failed: fopen(file, \"r\") != nullptr. : " + err,
+               PCHECK(fopen(file, "r") != nullptr));
 
-  EXPECT_CHECK(
-      "Check failed: fopen(file, \"r\") != nullptr."
-      " foo: " +
-          err,
-      PCHECK(fopen(file, "r") != nullptr) << "foo");
+  EXPECT_CHECK("Check failed: fopen(file, \"r\") != nullptr. foo: " + err,
+               PCHECK(fopen(file, "r") != nullptr) << "foo");
 
-  EXPECT_DCHECK(
-      "DCHECK failed: fopen(file, \"r\") != nullptr."
-      " : " +
-          err,
-      DPCHECK(fopen(file, "r") != nullptr));
+  EXPECT_DCHECK("DCHECK failed: fopen(file, \"r\") != nullptr. : " + err,
+                DPCHECK(fopen(file, "r") != nullptr));
 
-  EXPECT_DCHECK(
-      "DCHECK failed: fopen(file, \"r\") != nullptr."
-      " foo: " +
-          err,
-      DPCHECK(fopen(file, "r") != nullptr) << "foo");
+  EXPECT_DCHECK("DCHECK failed: fopen(file, \"r\") != nullptr. foo: " + err,
+                DPCHECK(fopen(file, "r") != nullptr) << "foo");
 }
 
 TEST(CheckDeathTest, CheckOp) {
@@ -619,7 +607,7 @@
   EXPECT_LOG_ERROR_WITH_FILENAME(base::Location::Current().file_name(),
                                  base::Location::Current().line_number(),
                                  NOTIMPLEMENTED() << "foo",
-                                 expected_msg + "foo\n");
+                                 expected_msg + ". foo\n");
 #else
   // Expect nothing.
   EXPECT_NO_LOG(NOTIMPLEMENTED() << "foo");
@@ -632,7 +620,7 @@
 
 TEST(CheckTest, NotImplementedLogOnce) {
   static const std::string expected_msg =
-      kNotImplementedMessage + "void (anonymous namespace)::NiLogOnce()\n";
+      kNotImplementedMessage + "void (anonymous namespace)::NiLogOnce(). \n";
 
 #if DCHECK_IS_ON()
   EXPECT_LOG_ERROR_WITH_FILENAME(base::Location::Current().file_name(),
@@ -654,16 +642,17 @@
 TEST(CheckTest, NotImplementedLogOnceWithStreamedParams) {
   static const std::string expected_msg1 =
       kNotImplementedMessage +
-      "void (anonymous namespace)::NiLogTenTimesWithStream() iteration: 0\n";
+      "void (anonymous namespace)::NiLogTenTimesWithStream(). "
+      " iteration: 0\n";
 
 #if DCHECK_IS_ON()
   // Expect LOG(ERROR) with streamed params intact, exactly once.
   EXPECT_LOG_ERROR_WITH_FILENAME(base::Location::Current().file_name(),
-                                 base::Location::Current().line_number() - 13,
+                                 base::Location::Current().line_number() - 14,
                                  NiLogTenTimesWithStream(), expected_msg1);
   // A different NOTIMPLEMENTED_LOG_ONCE() call is still logged.
   static const std::string expected_msg2 =
-      kNotImplementedMessage + __PRETTY_FUNCTION__ + "tree fish\n";
+      kNotImplementedMessage + __PRETTY_FUNCTION__ + ". tree fish\n";
   EXPECT_LOG_ERROR_WITH_FILENAME(base::Location::Current().file_name(),
                                  base::Location::Current().line_number(),
                                  NOTIMPLEMENTED_LOG_ONCE() << "tree fish",