diff --git a/source/parsing/Lexer.cpp b/source/parsing/Lexer.cpp
index 6d76df7c9..775f55808 100644
--- a/source/parsing/Lexer.cpp
+++ b/source/parsing/Lexer.cpp
@@ -1070,7 +1070,6 @@ Token Lexer::lexApostrophe() {
             return create(TokenKind::UnbasedUnsizedLiteral, logic_t::x);
         case 'Z':
         case 'z':
-        case '?':
             advance();
             return create(TokenKind::UnbasedUnsizedLiteral, logic_t::z);
         case 's':
diff --git a/source/parsing/Parser_expressions.cpp b/source/parsing/Parser_expressions.cpp
index 6a7759cb0..123b7910b 100644
--- a/source/parsing/Parser_expressions.cpp
+++ b/source/parsing/Parser_expressions.cpp
@@ -91,7 +91,11 @@ ExpressionSyntax& Parser::parseSubExpression(bitmask<ExpressionOptions> options,
         if (isNewExpr(leftOperand))
             return parseNewExpression(leftOperand->as<NameSyntax>(), options);
 
-        leftOperand = &parsePostfixExpression(*leftOperand, options);
+        // Don't try to parse postfix if we didn't find a valid primary to begin with.
+        if (leftOperand->kind != SyntaxKind::IdentifierName ||
+            !leftOperand->as<IdentifierNameSyntax>().identifier.isMissing()) {
+            leftOperand = &parsePostfixExpression(*leftOperand, options);
+        }
     }
 
     options &= ~ExpressionOptions::AllowSuperNewCall;
diff --git a/tests/unittests/parsing/ExpressionParsingTests.cpp b/tests/unittests/parsing/ExpressionParsingTests.cpp
index 51662a664..797da290a 100644
--- a/tests/unittests/parsing/ExpressionParsingTests.cpp
+++ b/tests/unittests/parsing/ExpressionParsingTests.cpp
@@ -978,3 +978,16 @@ endclass
     REQUIRE(diagnostics.size() == 1);
     CHECK(diagnostics[0].code == diag::WrongLanguageVersion);
 }
+
+TEST_CASE("Unbased unsized question mark parsing") {
+    auto& text = R"(
+module bug(input logic [1:0] a, input logic s, output logic [1:0]y);
+    assign y = s? a: '?;
+endmodule
+)";
+
+    parseCompilationUnit(text);
+
+    REQUIRE(diagnostics.size() == 1);
+    CHECK(diagnostics[0].code == diag::ExpectedExpression);
+}