diff --git a/Lib/_pydatetime.py b/Lib/_pydatetime.py
index 600a7e08345a82..ed8a5cdfaf1cde 100644
--- a/Lib/_pydatetime.py
+++ b/Lib/_pydatetime.py
@@ -431,7 +431,7 @@ def _parse_hh_mm_ss_ff(tstr):
 
     if pos < len_str:
         if tstr[pos] not in '.,':
-            raise ValueError("Invalid microsecond component")
+            raise ValueError("Invalid microsecond separator")
         else:
             pos += 1
 
@@ -489,7 +489,7 @@ def _parse_isoformat_time(tstr):
         # HH:MM:SS            len: 8
         # HH:MM:SS.f+         len: 10+
 
-        if len(tzstr) in (0, 1, 3):
+        if len(tzstr) in (0, 1, 3) or tstr[tz_pos-1] == 'Z':
             raise ValueError("Malformed time zone string")
 
         tz_comps = _parse_hh_mm_ss_ff(tzstr)
diff --git a/Lib/test/datetimetester.py b/Lib/test/datetimetester.py
index d1ef6339789d20..b670973a71c748 100644
--- a/Lib/test/datetimetester.py
+++ b/Lib/test/datetimetester.py
@@ -3533,6 +3533,8 @@ def test_fromisoformat_fails_datetime(self):
             '2009-04-32T24:00:00.000000',  # Day is invalid before wrapping due to 24:00
             '2009-13-01T24:00:00.000000',  # Month is invalid before wrapping due to 24:00
             '9999-12-31T24:00:00.000000',  # Year is invalid after wrapping due to 24:00
+            '2009-04-19T12:30Z12:00',      # Extra time zone info after Z
+            '2009-04-19T12:30:45:334034',  # Invalid microsecond separator
         ]
 
         for bad_str in bad_strs:
@@ -4658,6 +4660,7 @@ def test_fromisoformat_time_examples(self):
             ('00:00:00.000', self.theclass(0, 0)),
             ('000000.000000', self.theclass(0, 0)),
             ('00:00:00.000000', self.theclass(0, 0)),
+            ('00:00:00,100000', self.theclass(0, 0, 0, 100000)),
             ('1200', self.theclass(12, 0)),
             ('12:00', self.theclass(12, 0)),
             ('120000', self.theclass(12, 0)),
@@ -4725,6 +4728,8 @@ def test_fromisoformat_fails(self):
             '12:30:45.123456+12:00:30a',    # Extra at end of full time
             '12.5',                     # Decimal mark at end of hour
             '12:30,5',                  # Decimal mark at end of minute
+            '12:30:45.123456Z12:00',    # Extra time zone info after Z
+            '12:30:45:334034',          # Invalid microsecond separator
         ]
 
         for bad_str in bad_strs:
diff --git a/Misc/NEWS.d/next/Library/2025-02-14-23-38-03.gh-issue-127260.dXQ8P0.rst b/Misc/NEWS.d/next/Library/2025-02-14-23-38-03.gh-issue-127260.dXQ8P0.rst
new file mode 100644
index 00000000000000..453aa4a8678fe4
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-02-14-23-38-03.gh-issue-127260.dXQ8P0.rst
@@ -0,0 +1,4 @@
+Forbid the use of colon (":") as a fractional component separator and other
+improvements to the consistency of error raising between the C and Python
+implementaitons of :meth:`datetime.time.fromisoformat` and
+:meth:`datetime.datetime.fromisoformat`. Patch by Semyon Moroz.
diff --git a/Modules/_datetimemodule.c b/Modules/_datetimemodule.c
index 8b202cc51788a9..b5ccf2f7b65d63 100644
--- a/Modules/_datetimemodule.c
+++ b/Modules/_datetimemodule.c
@@ -1014,6 +1014,9 @@ parse_hh_mm_ss_ff(const char *tstr, const char *tstr_end, int *hour,
             return c != '\0';
         }
         else if (has_separator && (c == ':')) {
+            if (i == 2) {
+                return -4;  // Malformed microsecond separator
+            }
             continue;
         }
         else if (c == '.' || c == ',') {