diff --git a/ddtrace/appsec/_iast/_taint_tracking/aspects.py b/ddtrace/appsec/_iast/_taint_tracking/aspects.py
index 8b52878f275..fa2f512f81a 100644
--- a/ddtrace/appsec/_iast/_taint_tracking/aspects.py
+++ b/ddtrace/appsec/_iast/_taint_tracking/aspects.py
@@ -449,8 +449,8 @@ def format_value_aspect(
             return format(new_text, format_spec)
         return format(new_text)
 
-    try:
-        if format_spec:
+    if format_spec:
+        try:
             # Apply formatting
             text_ranges = get_tainted_ranges(new_text)
             if text_ranges:
@@ -466,11 +466,11 @@ def format_value_aspect(
                     return ("{:%s}" % format_spec).format(new_text)
             else:
                 return ("{:%s}" % format_spec).format(new_text)
-        else:
-            return format(new_text)
-    except Exception as e:
-        iast_propagation_error_log(f"format_value_aspect. {e}")
-        return new_text
+        except Exception as e:
+            iast_propagation_error_log(f"format_value_aspect. {e}")
+            return ("{:%s}" % format_spec).format(new_text)
+
+    return format(new_text)
 
 
 def incremental_translation(self, incr_coder, funcode, empty):
diff --git a/releasenotes/notes/iast-fstring-exception-d460a37b6e44f972.yaml b/releasenotes/notes/iast-fstring-exception-d460a37b6e44f972.yaml
new file mode 100644
index 00000000000..a22008a34ca
--- /dev/null
+++ b/releasenotes/notes/iast-fstring-exception-d460a37b6e44f972.yaml
@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    IAST: Fixes a bug where invalid f-strings didn’t raise the expected "Unknown format code" error when IAST was enabled.
diff --git a/tests/appsec/iast/aspects/test_str_py3.py b/tests/appsec/iast/aspects/test_str_py3.py
index ba468c34286..b4a4291ea8d 100644
--- a/tests/appsec/iast/aspects/test_str_py3.py
+++ b/tests/appsec/iast/aspects/test_str_py3.py
@@ -1,3 +1,5 @@
+from hypothesis import given
+from hypothesis.strategies import text
 import pytest
 
 from ddtrace.appsec._iast._taint_tracking import as_formatted_evidence
@@ -10,6 +12,17 @@
 mod_py3 = _iast_patched_module("benchmarks.bm.iast_fixtures.str_methods_py3")
 
 
+@given(text())
+def test_int_fstring_zero_padding_text(text):
+    with pytest.raises(ValueError) as excinfo:
+        f"{text:05d}"
+    assert str(excinfo.value) == "Unknown format code 'd' for object of type 'str'"
+
+    with pytest.raises(ValueError) as excinfo:
+        mod_py3.do_zero_padding_fstring(text)
+    assert str(excinfo.value) == "Unknown format code 'd' for object of type 'str'"
+
+
 class TestOperatorsReplacement(BaseReplacement):
     @staticmethod
     def test_taint():  # type: () -> None