diff --git a/lib/checkuninitvar.cpp b/lib/checkuninitvar.cpp
index 60f49c4a2..05fe4523f 100644
--- a/lib/checkuninitvar.cpp
+++ b/lib/checkuninitvar.cpp
@@ -412,7 +412,7 @@ private:
                 if (var2->isPointer())
                     checks.push_back(new UninitVar(owner, var2, symbolDatabase, isC));
                 else if (var2->typeEndToken()->str() != ">") {
-                    bool stdtype = isC;
+                    bool stdtype = false;  // TODO: change to isC to handle unknown types better
                     for (const Token* tok2 = var2->typeStartToken(); tok2 != var2->nameToken(); tok2 = tok2->next()) {
                         if (tok2->isStandardType()) {
                             stdtype = true;
diff --git a/test/testuninitvar.cpp b/test/testuninitvar.cpp
index fd18f8e3e..2167ce886 100644
--- a/test/testuninitvar.cpp
+++ b/test/testuninitvar.cpp
@@ -84,13 +84,6 @@ private:
                        "}\n");
         ASSERT_EQUALS("[test.cpp:3]: (error) Uninitialized variable: a\n", errout.str());
 
-        checkUninitVar("void foo() {\n"
-                       "    dfs a;\n"
-                       "    b = c - a;\n"
-                       "}\n",
-                       "test.c");
-        ASSERT_EQUALS("[test.c:3]: (error) Uninitialized variable: a\n", errout.str());
-
         checkUninitVar("void foo() {\n"
                        "    int a;\n"
                        "    b = a - c;\n"
@@ -310,7 +303,15 @@ private:
                            "    return ret;\n"
                            "}\n",
                            "test.c");
-            ASSERT_EQUALS("[test.c:4]: (error) Uninitialized variable: ret\n", errout.str());
+            TODO_ASSERT_EQUALS("[test.c:4]: (error) Uninitialized variable: ret\n", "", errout.str());
+
+            // #3916 - avoid false positive
+            checkUninitVar("void f(float x) {\n"
+                           "  union lf { long l; float f; } u_lf;\n"
+                           "  float hx = (u_lf.f = (x), u_lf.l);\n"
+                           "}\n",
+                           "test.c");
+            ASSERT_EQUALS("", errout.str());
         }
 
         checkUninitVar("void a()\n"