diff --git a/arrow/arrow.py b/arrow/arrow.py
index eecf2326..ada8efcd 100644
--- a/arrow/arrow.py
+++ b/arrow/arrow.py
@@ -773,7 +773,7 @@ def interval(
             (<Arrow [2013-05-05T14:00:00+00:00]>, <Arrow [2013-05-05T15:59:59.999999+00:00]>)
             (<Arrow [2013-05-05T16:00:00+00:00]>, <Arrow [2013-05-05T17:59:59.999999+00:0]>)
         """
-        if interval < 1:
+        if isinstance(interval, bool) or not isinstance(interval, int) or interval < 1:
             raise ValueError("interval has to be a positive integer")
 
         spanRange = iter(
@@ -1367,7 +1367,7 @@ def dehumanize(self, input_string: str, locale: str = "en_us") -> "Arrow":
 
         """
 
-        # Create a locale object based off given local
+        # Create a locale object based off given localee
         locale_obj = locales.get_locale(locale)
 
         # Check to see if locale is supported
@@ -1380,6 +1380,14 @@ def dehumanize(self, input_string: str, locale: str = "en_us") -> "Arrow":
 
         current_time = self.fromdatetime(self._datetime)
 
+        # Reject non-string input before looking up locale-specific patterns.
+        # This keeps the public error stable even when a locale stores timeframes
+        # in a mapping that would otherwise be searched with regex operations.
+        if not isinstance(input_string, str):
+            raise TypeError(
+                f"input_string must be str, not {type(input_string).__name__}."
+            )
+
         # Create an object containing the relative time info
         time_object_info = dict.fromkeys(
             ["seconds", "minutes", "hours", "days", "weeks", "months", "years"], 0
@@ -1392,7 +1400,7 @@ def dehumanize(self, input_string: str, locale: str = "en_us") -> "Arrow":
         )
 
         # Create a regex pattern object for numbers
-        num_pattern = re.compile(r"\d+")
+        num_pattern = re.compile(r"\d+(?:\.\d+)?")
 
         # Search input string for each time unit within locale
         for unit, unit_object in locale_obj.timeframes.items():
@@ -1408,7 +1416,7 @@ def dehumanize(self, input_string: str, locale: str = "en_us") -> "Arrow":
             for time_delta, time_string in strings_to_search.items():
                 # Replace {0} with regex \d representing digits
                 search_string = str(time_string)
-                search_string = search_string.format(r"\d+")
+                search_string = search_string.format(r"\d+(?:\.\d+)?")
 
                 # Create search pattern and find within string
                 pattern = re.compile(rf"(^|\b|\d){search_string}")
@@ -1428,7 +1436,7 @@ def dehumanize(self, input_string: str, locale: str = "en_us") -> "Arrow":
                         1 if not time_delta.isnumeric() else abs(int(time_delta))
                     )
                 else:
-                    change_value = int(num_match.group())
+                    change_value = float(num_match.group())
 
                 # No time to update if now is the unit
                 if unit == "now":
diff --git a/arrow/parser.py b/arrow/parser.py
index fc3774b0..ec48fbc4 100644
--- a/arrow/parser.py
+++ b/arrow/parser.py
@@ -844,6 +844,7 @@ def _parse_multiformat(self, string: str, formats: Iterable[str]) -> datetime:
         :raises ParserError: If no format matches the input string.
         """
         _datetime: Optional[datetime] = None
+        formats = list(formats)
 
         for fmt in formats:
             try:
diff --git a/tests/test_arrow.py b/tests/test_arrow.py
index b595e4e2..b52c4814 100644
--- a/tests/test_arrow.py
+++ b/tests/test_arrow.py
@@ -1557,11 +1557,12 @@ def test_small_interval_exact_open_bounds(self):
 
 
 class TestArrowInterval:
-    def test_incorrect_input(self):
-        with pytest.raises(ValueError):
+    @pytest.mark.parametrize("interval", [0, -1, 1.5, True])
+    def test_incorrect_input(self, interval):
+        with pytest.raises(ValueError, match="positive integer"):
             list(
                 arrow.Arrow.interval(
-                    "month", datetime(2013, 1, 2), datetime(2013, 4, 15), 0
+                    "month", datetime(2013, 1, 2), datetime(2013, 4, 15), interval
                 )
             )
 
@@ -2606,6 +2607,12 @@ def slavic_locales() -> List[str]:
 
 
 class TestArrowDehumanize:
+    def test_non_string_input_raises_type_error(self):
+        arw = arrow.Arrow.utcnow()
+
+        with pytest.raises(TypeError, match="input_string must be str"):
+            arw.dehumanize(None)
+
     def test_now(self, locale_list_no_weeks: List[str]):
         for lang in locale_list_no_weeks:
             arw = arrow.Arrow(2000, 6, 18, 5, 55, 0)
@@ -2832,6 +2839,12 @@ def test_mixed_granularity_day_hour(self, locale_list_no_weeks: List[str]):
             assert arw.dehumanize(past_string, locale=lang) == past
             assert arw.dehumanize(future_string, locale=lang) == future
 
+    def test_decimal_unit_quantity_preserves_fraction(self):
+        arw = arrow.Arrow(2000, 6, 18, 5, 55, 0)
+
+        assert arw.dehumanize("in 1.5 hours") == arw.shift(hours=1.5)
+        assert arw.dehumanize("1.5 hours ago") == arw.shift(hours=-1.5)
+
     # Test to make sure unsupported locales error out
     def test_unsupported_locale(self):
         arw = arrow.Arrow(2000, 6, 18, 5, 55, 0)
diff --git a/tests/test_parser.py b/tests/test_parser.py
index 7038d880..23b4aeb6 100644
--- a/tests/test_parser.py
+++ b/tests/test_parser.py
@@ -61,6 +61,15 @@ def test_parse_multiformat_all_fail(self, mocker):
         with pytest.raises(parser.ParserError):
             self.parser._parse_multiformat("str", ["fmt_a", "fmt_b"])
 
+    def test_parse_multiformat_reports_generator_formats(self, mocker):
+        mocker.patch(
+            "arrow.parser.DateTimeParser.parse",
+            side_effect=parser.ParserMatchError,
+        )
+
+        with pytest.raises(parser.ParserError, match="fmt_a, fmt_b"):
+            self.parser._parse_multiformat("str", (fmt for fmt in ("fmt_a", "fmt_b")))
+
     def test_parse_multiformat_unself_expected_fail(self, mocker):
         class UnselfExpectedError(Exception):
             pass