diff --git a/src/parsers/conan.rs b/src/parsers/conan.rs
index cb80b3abd..2f79d1184 100644
--- a/src/parsers/conan.rs
+++ b/src/parsers/conan.rs
@@ -475,16 +475,18 @@ fn parse_conan_reference(ref_str: &str) -> Option<Dependency> {
         }
     });
 
-    let purl = if let Some(v) = version.as_deref() {
-        PackageUrl::new("conan", name)
-            .map(|mut p| {
+    // A range constraint is not a PURL version, so ranged and bare references
+    // both fall through to a name-only PURL and keep the constraint in
+    // `extracted_requirement`.
+    let purl = version
+        .as_deref()
+        .and_then(|v| {
+            PackageUrl::new("conan", name).ok().map(|mut p| {
                 let _ = p.with_version(v);
                 p.to_string()
             })
-            .unwrap_or_else(|_| format!("pkg:conan/{}", name))
-    } else {
-        format!("pkg:conan/{}", name)
-    };
+        })
+        .unwrap_or_else(|| format!("pkg:conan/{}", name));
 
     let is_pinned = version_spec
         .as_ref()
diff --git a/src/parsers/poetry_lock.rs b/src/parsers/poetry_lock.rs
index facc2e6f7..4a8a25302 100644
--- a/src/parsers/poetry_lock.rs
+++ b/src/parsers/poetry_lock.rs
@@ -407,16 +407,11 @@ fn create_pypi_purl(name: &str, version: Option<&str>) -> Option<String> {
         return Some(truncate_field(build_manual_pypi_purl(name, version)));
     }
 
-    if let Ok(mut purl) = PackageUrl::new(PoetryLockParser::PACKAGE_TYPE.as_str(), name) {
-        if let Some(version) = version
-            && purl.with_version(version).is_err()
-        {
-            return None;
-        }
-        return Some(truncate_field(purl.to_string()));
+    let mut purl = PackageUrl::new(PoetryLockParser::PACKAGE_TYPE.as_str(), name).ok()?;
+    if let Some(version) = version {
+        purl.with_version(version).ok()?;
     }
-
-    Some(truncate_field(build_manual_pypi_purl(name, version)))
+    Some(truncate_field(purl.to_string()))
 }
 
 fn build_manual_pypi_purl(name: &str, version: Option<&str>) -> String {
diff --git a/src/parsers/pylock_toml.rs b/src/parsers/pylock_toml.rs
index c34d22238..a3777b7b8 100644
--- a/src/parsers/pylock_toml.rs
+++ b/src/parsers/pylock_toml.rs
@@ -734,23 +734,11 @@ fn build_pypi_urls(
 }
 
 fn create_pypi_purl(name: &str, version: Option<&str>) -> Option<String> {
-    if let Ok(mut purl) = PackageUrl::new(PylockTomlParser::PACKAGE_TYPE.as_str(), name) {
-        if let Some(version) = version
-            && purl.with_version(version).is_err()
-        {
-            return None;
-        }
-        return Some(truncate_field(purl.to_string()));
-    }
-
-    let mut purl = format!("pkg:pypi/{}", name);
-    if let Some(version) = version
-        && !version.is_empty()
-    {
-        purl.push('@');
-        purl.push_str(version);
+    let mut purl = PackageUrl::new(PylockTomlParser::PACKAGE_TYPE.as_str(), name).ok()?;
+    if let Some(version) = version {
+        purl.with_version(version).ok()?;
     }
-    Some(truncate_field(purl))
+    Some(truncate_field(purl.to_string()))
 }
 
 fn toml_value_to_json(value: &TomlValue) -> JsonValue {
diff --git a/src/parsers/python/pyproject.rs b/src/parsers/python/pyproject.rs
index cde2ee3c2..fb53b4fb5 100644
--- a/src/parsers/python/pyproject.rs
+++ b/src/parsers/python/pyproject.rs
@@ -723,7 +723,7 @@ fn build_poetry_group_dependency(
     let pinned_version = version_spec
         .as_deref()
         .and_then(extract_exact_pinned_version);
-    let purl = build_python_dependency_purl(&normalized_name, pinned_version.as_deref())?;
+    let purl = build_python_dependency_purl(&normalized_name, pinned_version.as_deref());
 
     let mut extra_data = HashMap::new();
     if let Some(marker) = marker {
@@ -737,7 +737,7 @@ fn build_poetry_group_dependency(
     }
 
     Some(Dependency {
-        purl: Some(purl),
+        purl,
         extracted_requirement: version_spec,
         scope: scope.map(|value| value.to_string()),
         is_runtime: Some(!is_optional),
@@ -779,7 +779,7 @@ fn build_pyproject_array_dependency(
         .as_deref()
         .and_then(extract_exact_pinned_version);
 
-    let purl = build_python_dependency_purl(&name, pinned_version.as_deref())?;
+    let purl = build_python_dependency_purl(&name, pinned_version.as_deref());
 
     let mut extra_data = HashMap::new();
     if let Some(marker) = parsed.marker {
@@ -795,7 +795,7 @@ fn build_pyproject_array_dependency(
     let extracted_requirement = parsed.specifiers.or(parsed.url);
 
     Some(Dependency {
-        purl: Some(purl),
+        purl,
         extracted_requirement: extracted_requirement.clone(),
         scope: scope.map(|s| s.to_string()),
         is_runtime: Some(!is_optional),
diff --git a/src/parsers/python/scan_test.rs b/src/parsers/python/scan_test.rs
index f5907bc73..76a4aaea2 100644
--- a/src/parsers/python/scan_test.rs
+++ b/src/parsers/python/scan_test.rs
@@ -771,4 +771,41 @@ license = { file = "LICENSE.txt" }
             1
         );
     }
+
+    #[test]
+    fn test_setup_cfg_scan_keeps_a_purl_less_dependency_through_assembly() {
+        // A requirement whose name is not a distribution name yields no PURL, and
+        // assembly must still carry it to the top level rather than dropping the
+        // only record of it. `extracted_requirement` is where the raw text lives,
+        // so a purl-less entry is the honest result, not a lost one.
+        let temp_dir = tempfile::TempDir::new().expect("create temp dir");
+        fs::write(
+            temp_dir.path().join("setup.cfg"),
+            "[metadata]\nname = demo\nversion = 1.0.0\n\n[options]\ninstall_requires =\n    a/b==2.0\n    requests>=2.0\n",
+        )
+        .expect("write setup.cfg");
+
+        let (_files, result) = scan_and_assemble(temp_dir.path());
+
+        assert_dependency_present(&result.dependencies, "pkg:pypi/requests", "setup.cfg");
+
+        let purl_less = result
+            .dependencies
+            .iter()
+            .find(|dependency| dependency.extracted_requirement.as_deref() == Some("a/b==2.0"))
+            .expect("the purl-less dependency should survive assembly");
+        assert_eq!(purl_less.purl, None);
+        assert!(
+            purl_less.datafile_path.ends_with("setup.cfg"),
+            "it should stay attributed to its datafile, got {}",
+            purl_less.datafile_path
+        );
+        assert!(
+            result.dependencies.iter().all(|dependency| dependency
+                .purl
+                .as_deref()
+                .is_none_or(|purl| !purl.contains("a/b"))),
+            "the invalid name must not reappear as a purl anywhere"
+        );
+    }
 }
diff --git a/src/parsers/python/setup_cfg.rs b/src/parsers/python/setup_cfg.rs
index aa8ad470d..9c531feff 100644
--- a/src/parsers/python/setup_cfg.rs
+++ b/src/parsers/python/setup_cfg.rs
@@ -254,13 +254,13 @@ fn build_setup_cfg_dependency(req: &str, scope: &str, is_optional: bool) -> Opti
             .as_deref()
             .map(|requirement| requirement.trim_start_matches('='))
             .and_then(|version| build_python_dependency_purl(&name, Some(version)))
-            .or_else(|| build_python_dependency_purl(&name, None))?
+            .or_else(|| build_python_dependency_purl(&name, None))
     } else {
-        build_python_dependency_purl(&name, None)?
+        build_python_dependency_purl(&name, None)
     };
 
     Some(Dependency {
-        purl: Some(purl),
+        purl,
         extracted_requirement: Some(normalize_setup_cfg_requirement(trimmed)),
         scope: Some(scope.to_string()),
         is_runtime: Some(true),
diff --git a/src/parsers/python/test.rs b/src/parsers/python/test.rs
index 7f530470e..cfbd8a911 100644
--- a/src/parsers/python/test.rs
+++ b/src/parsers/python/test.rs
@@ -3139,6 +3139,42 @@ install_requires =
         }));
     }
 
+    #[test]
+    fn test_setup_cfg_dependency_name_that_is_not_a_distribution_name_yields_no_purl() {
+        // `install_requires` is free-form text, so a name containing `/` reached
+        // the PURL verbatim as `pkg:pypi/a/b@2.0` — which no PURL parser accepts,
+        // since pypi prohibits a namespace. The raw text stays in
+        // `extracted_requirement`, so nothing is lost by declining the PURL.
+        let content = r#"
+[metadata]
+name = test-package
+version = 1.0.0
+
+[options]
+install_requires =
+    a/b==2.0
+    requests>=2.0
+"#;
+
+        let (_temp_dir, file_path) = create_temp_file(content, "setup.cfg");
+        let package_data = PythonParser::extract_first_package(&file_path);
+
+        let invalid = package_data
+            .dependencies
+            .iter()
+            .find(|dependency| dependency.extracted_requirement.as_deref() == Some("a/b==2.0"))
+            .expect("the unparsable requirement should still be reported");
+        assert_eq!(invalid.purl, None);
+
+        assert!(
+            package_data
+                .dependencies
+                .iter()
+                .any(|dependency| { dependency.purl.as_deref() == Some("pkg:pypi/requests") }),
+            "the valid requirement in the same file must be unaffected"
+        );
+    }
+
     #[test]
     fn test_setup_cfg_dependency_preserves_pinned_version_in_purl() {
         let content = r#"
diff --git a/src/parsers/python/utils.rs b/src/parsers/python/utils.rs
index 4fb918872..c8c8b5e84 100644
--- a/src/parsers/python/utils.rs
+++ b/src/parsers/python/utils.rs
@@ -205,7 +205,7 @@ pub(super) fn build_python_dependency(
         default_scope,
         default_optional,
     );
-    let purl = build_python_dependency_purl(&name, None)?;
+    let purl = build_python_dependency_purl(&name, None);
 
     let is_pinned = requirement
         .as_deref()
@@ -215,7 +215,7 @@ pub(super) fn build_python_dependency(
             .as_deref()
             .map(|req| req.trim_start_matches('='))
             .and_then(|version| build_python_dependency_purl(&name, Some(version)))
-            .unwrap_or(purl)
+            .or(purl)
     } else {
         purl
     };
@@ -227,7 +227,7 @@ pub(super) fn build_python_dependency(
     }
 
     Some(Dependency {
-        purl: Some(purl),
+        purl,
         extracted_requirement: requirement,
         scope: Some(parsed.scope),
         is_runtime: Some(true),
@@ -247,20 +247,28 @@ pub(super) fn normalize_python_dependency_name(name: &str) -> String {
     normalize_python_distribution_name(name)
 }
 
+/// Builds the PyPI PURL for a dependency name, or `None` when the name is not a
+/// distribution name.
+///
+/// The check replaces a `PackageUrl::new(…).ok()` gate that never rejected
+/// anything: that call validates the *type*, which is a constant here, and the
+/// PURL was then assembled with `format!` anyway. Names reaching this from
+/// `setup.cfg` are taken from free-form text, so `install_requires = a/b==2.0`
+/// produced `pkg:pypi/a/b@2.0` — a PURL no parser accepts, since pypi prohibits a
+/// namespace.
 pub(super) fn build_python_dependency_purl(name: &str, version: Option<&str>) -> Option<String> {
     let normalized_name = normalize_python_dependency_name(name);
+    if !crate::parsers::pep508::is_valid_distribution_name(&normalized_name) {
+        return None;
+    }
 
-    PackageUrl::new(PythonParser::PACKAGE_TYPE.as_str(), &normalized_name)
-        .ok()
-        .map(|_| match version {
-            Some(version) => {
-                format!(
-                    "pkg:pypi/{normalized_name}@{}",
-                    encode_python_dependency_purl_version(version)
-                )
-            }
-            None => format!("pkg:pypi/{normalized_name}"),
-        })
+    Some(match version {
+        Some(version) => format!(
+            "pkg:pypi/{normalized_name}@{}",
+            encode_python_dependency_purl_version(version)
+        ),
+        None => format!("pkg:pypi/{normalized_name}"),
+    })
 }
 
 fn encode_python_dependency_purl_version(version: &str) -> String {
@@ -502,10 +510,10 @@ fn parse_setup_py_dep_list(deps_str: &str, scope: &str, is_optional: bool) -> Ve
             }
 
             let name = extract_setup_cfg_dependency_name(dep_str)?;
-            let purl = build_python_dependency_purl(&name, None)?;
+            let purl = build_python_dependency_purl(&name, None);
 
             Some(Dependency {
-                purl: Some(purl),
+                purl,
                 extracted_requirement: Some(dep_str.to_string()),
                 scope: Some(scope.to_string()),
                 is_runtime: Some(true),
diff --git a/src/parsers/uv_lock.rs b/src/parsers/uv_lock.rs
index e0f7ad90a..cb21bbe21 100644
--- a/src/parsers/uv_lock.rs
+++ b/src/parsers/uv_lock.rs
@@ -935,16 +935,11 @@ fn create_pypi_purl(name: &str, version: Option<&str>) -> Option<String> {
         return Some(truncate_field(build_manual_pypi_purl(name, version)));
     }
 
-    if let Ok(mut purl) = PackageUrl::new(UvLockParser::PACKAGE_TYPE.as_str(), name) {
-        if let Some(version) = version
-            && purl.with_version(version).is_err()
-        {
-            return None;
-        }
-        return Some(truncate_field(purl.to_string()));
+    let mut purl = PackageUrl::new(UvLockParser::PACKAGE_TYPE.as_str(), name).ok()?;
+    if let Some(version) = version {
+        purl.with_version(version).ok()?;
     }
-
-    Some(truncate_field(build_manual_pypi_purl(name, version)))
+    Some(truncate_field(purl.to_string()))
 }
 
 fn build_manual_pypi_purl(name: &str, version: Option<&str>) -> String {