diff --git a/csharp/ql/lib/semmle/code/csharp/controlflow/internal/Completion.qll b/csharp/ql/lib/semmle/code/csharp/controlflow/internal/Completion.qll
index a470d0c4b8a2..6fed45cdf84d 100644
--- a/csharp/ql/lib/semmle/code/csharp/controlflow/internal/Completion.qll
+++ b/csharp/ql/lib/semmle/code/csharp/controlflow/internal/Completion.qll
@@ -293,6 +293,8 @@ private predicate isMatchingConstant(PatternExpr pe, boolean value) {
   value = true
   or
   exists(Type t, Type strippedType |
+    not t instanceof UnknownType and
+    not strippedType instanceof UnknownType and
     typePatternMustHaveMatchingCompletion(pe, t, strippedType) and
     not typePatternCommonSubType(t, strippedType) and
     value = false
diff --git a/csharp/ql/src/change-notes/2025-03-10-unknown-type-matching.md b/csharp/ql/src/change-notes/2025-03-10-unknown-type-matching.md
new file mode 100644
index 000000000000..634f46067007
--- /dev/null
+++ b/csharp/ql/src/change-notes/2025-03-10-unknown-type-matching.md
@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* Increase query precision for `cs/useless-assignment-to-local` and `cs/constant-condition` when *unknown* types are involved (mostly relevant for `build-mode: none` databases).
diff --git a/csharp/ql/test/query-tests/standalone/Bad Practices/Control-Flow/ConstantCondition/ConstantCondition.cs b/csharp/ql/test/query-tests/standalone/Bad Practices/Control-Flow/ConstantCondition/ConstantCondition.cs
new file mode 100644
index 000000000000..6f40759b3e67
--- /dev/null
+++ b/csharp/ql/test/query-tests/standalone/Bad Practices/Control-Flow/ConstantCondition/ConstantCondition.cs	
@@ -0,0 +1,27 @@
+using System;
+
+partial class C1
+{
+    public C2 Prop { get; set; }
+}
+
+class C2 { }
+
+class ConstantMatching
+{
+    void M1()
+    {
+        var c1 = new C1();
+        if (c1.Prop is int) // $ Alert
+        {
+        }
+
+        // Should not be considered a constant condition as
+        // we don't know anything about D.
+        var d = new D();
+        if (d.Prop is C2)
+        {
+        }
+    }
+}
+
diff --git a/csharp/ql/test/query-tests/standalone/Bad Practices/Control-Flow/ConstantCondition/ConstantCondition.expected b/csharp/ql/test/query-tests/standalone/Bad Practices/Control-Flow/ConstantCondition/ConstantCondition.expected
new file mode 100644
index 000000000000..25ed39bebb72
--- /dev/null
+++ b/csharp/ql/test/query-tests/standalone/Bad Practices/Control-Flow/ConstantCondition/ConstantCondition.expected	
@@ -0,0 +1,2 @@
+| ConstantCondition.cs:15:13:15:26 | ... is ... | Condition always evaluates to 'false'. |
+| ConstantCondition.cs:15:24:15:26 | access to type Int32 | Pattern never matches. |
diff --git a/csharp/ql/test/query-tests/standalone/Bad Practices/Control-Flow/ConstantCondition/ConstantCondition.qlref b/csharp/ql/test/query-tests/standalone/Bad Practices/Control-Flow/ConstantCondition/ConstantCondition.qlref
new file mode 100644
index 000000000000..6692217230e0
--- /dev/null
+++ b/csharp/ql/test/query-tests/standalone/Bad Practices/Control-Flow/ConstantCondition/ConstantCondition.qlref	
@@ -0,0 +1,2 @@
+query: Bad Practices/Control-Flow/ConstantCondition.ql
+postprocess: utils/test/InlineExpectationsTestQuery.ql
diff --git a/csharp/ql/test/query-tests/standalone/IncomparableEquals/options b/csharp/ql/test/query-tests/standalone/Bad Practices/Control-Flow/ConstantCondition/options
similarity index 100%
rename from csharp/ql/test/query-tests/standalone/IncomparableEquals/options
rename to csharp/ql/test/query-tests/standalone/Bad Practices/Control-Flow/ConstantCondition/options
diff --git a/csharp/ql/test/query-tests/standalone/IncomparableEquals/IncomparableEquals.cs b/csharp/ql/test/query-tests/standalone/Likely Bugs/IncomparableEquals/IncomparableEquals.cs
similarity index 100%
rename from csharp/ql/test/query-tests/standalone/IncomparableEquals/IncomparableEquals.cs
rename to csharp/ql/test/query-tests/standalone/Likely Bugs/IncomparableEquals/IncomparableEquals.cs
diff --git a/csharp/ql/test/query-tests/standalone/IncomparableEquals/IncomparableEquals.expected b/csharp/ql/test/query-tests/standalone/Likely Bugs/IncomparableEquals/IncomparableEquals.expected
similarity index 100%
rename from csharp/ql/test/query-tests/standalone/IncomparableEquals/IncomparableEquals.expected
rename to csharp/ql/test/query-tests/standalone/Likely Bugs/IncomparableEquals/IncomparableEquals.expected
diff --git a/csharp/ql/test/query-tests/standalone/IncomparableEquals/IncomparableEquals.qlref b/csharp/ql/test/query-tests/standalone/Likely Bugs/IncomparableEquals/IncomparableEquals.qlref
similarity index 100%
rename from csharp/ql/test/query-tests/standalone/IncomparableEquals/IncomparableEquals.qlref
rename to csharp/ql/test/query-tests/standalone/Likely Bugs/IncomparableEquals/IncomparableEquals.qlref
diff --git a/csharp/ql/test/query-tests/standalone/ObjectComparison/options b/csharp/ql/test/query-tests/standalone/Likely Bugs/IncomparableEquals/options
similarity index 100%
rename from csharp/ql/test/query-tests/standalone/ObjectComparison/options
rename to csharp/ql/test/query-tests/standalone/Likely Bugs/IncomparableEquals/options
diff --git a/csharp/ql/test/query-tests/standalone/ObjectComparison/ObjectComparison.cs b/csharp/ql/test/query-tests/standalone/Likely Bugs/ObjectComparison/ObjectComparison.cs
similarity index 100%
rename from csharp/ql/test/query-tests/standalone/ObjectComparison/ObjectComparison.cs
rename to csharp/ql/test/query-tests/standalone/Likely Bugs/ObjectComparison/ObjectComparison.cs
diff --git a/csharp/ql/test/query-tests/standalone/ObjectComparison/ObjectComparison.expected b/csharp/ql/test/query-tests/standalone/Likely Bugs/ObjectComparison/ObjectComparison.expected
similarity index 100%
rename from csharp/ql/test/query-tests/standalone/ObjectComparison/ObjectComparison.expected
rename to csharp/ql/test/query-tests/standalone/Likely Bugs/ObjectComparison/ObjectComparison.expected
diff --git a/csharp/ql/test/query-tests/standalone/ObjectComparison/ObjectComparison.qlref b/csharp/ql/test/query-tests/standalone/Likely Bugs/ObjectComparison/ObjectComparison.qlref
similarity index 100%
rename from csharp/ql/test/query-tests/standalone/ObjectComparison/ObjectComparison.qlref
rename to csharp/ql/test/query-tests/standalone/Likely Bugs/ObjectComparison/ObjectComparison.qlref
diff --git a/csharp/ql/test/query-tests/standalone/Likely Bugs/ObjectComparison/options b/csharp/ql/test/query-tests/standalone/Likely Bugs/ObjectComparison/options
new file mode 100644
index 000000000000..7ba3811b2afb
--- /dev/null
+++ b/csharp/ql/test/query-tests/standalone/Likely Bugs/ObjectComparison/options	
@@ -0,0 +1 @@
+semmle-extractor-options: --standalone