diff --git a/Sources/ScreamURITemplate/Internal/Scanner.swift b/Sources/ScreamURITemplate/Internal/Scanner.swift
index 3db2b59..e93e1f1 100644
--- a/Sources/ScreamURITemplate/Internal/Scanner.swift
+++ b/Sources/ScreamURITemplate/Internal/Scanner.swift
@@ -48,26 +48,22 @@ struct Scanner {
         }
     }
 
-    private func checkUnterminated() throws(URITemplate.Error) {
-        if currentIndex == unicodeScalars.endIndex {
-            throw URITemplate.Error(type: .malformedTemplate, position: currentIndex, reason: "Unterminated Expression")
-        }
-    }
-
     private mutating func scanExpressionComponent() throws(URITemplate.Error) -> Component {
         assert(unicodeScalars[currentIndex] == "{")
         let expressionStartIndex = currentIndex
         currentIndex = unicodeScalars.index(after: currentIndex)
-        try checkUnterminated()
 
         let expressionOperator = try scanExpressionOperator()
-        try checkUnterminated()
         let variableList = try scanVariableList()
 
         return ExpressionComponent(expressionOperator: expressionOperator, variableList: variableList, templatePosition: expressionStartIndex)
     }
 
     private mutating func scanExpressionOperator() throws(URITemplate.Error) -> ExpressionOperator {
+        guard currentIndex < unicodeScalars.endIndex else {
+            return .simple
+        }
+
         let expressionOperator: ExpressionOperator
         if expressionOperatorCharacterSet.contains(unicodeScalars[currentIndex]) {
             guard let `operator` = ExpressionOperator(rawValue: unicodeScalars[currentIndex]) else {
@@ -87,15 +83,13 @@ struct Scanner {
         var complete = false
         while !complete {
             let variableName = try scanVariableName()
-
-            try checkUnterminated()
-
             let modifier = try scanVariableModifier()
-
-            try checkUnterminated()
-
             variableList.append(VariableSpec(name: variableName, modifier: modifier))
 
+            guard currentIndex < unicodeScalars.endIndex else {
+                throw URITemplate.Error(type: .malformedTemplate, position: currentIndex, reason: "Unterminated Expression")
+            }
+
             switch unicodeScalars[currentIndex] {
             case ",":
                 currentIndex = unicodeScalars.index(after: currentIndex)
@@ -134,6 +128,10 @@ struct Scanner {
     }
 
     private mutating func scanVariableModifier() throws(URITemplate.Error) -> VariableSpec.Modifier {
+        guard currentIndex < unicodeScalars.endIndex else {
+            return .none
+        }
+
         switch unicodeScalars[currentIndex] {
         case "*":
             currentIndex = unicodeScalars.index(after: currentIndex)
diff --git a/Tests/ScreamURITemplateTests/Tests.swift b/Tests/ScreamURITemplateTests/Tests.swift
index 5e3c75f..ae9ec7e 100644
--- a/Tests/ScreamURITemplateTests/Tests.swift
+++ b/Tests/ScreamURITemplateTests/Tests.swift
@@ -27,9 +27,13 @@ private struct TestVariableProvider: VariableProvider {
 }
 
 class Tests: XCTestCase {
-    func testUncompleteNotCrashing() throws {
-        // Use case: the user enters a template. This should not crash.
+    func testUnterminatedExpression() throws {
         XCTAssertThrowsError(try URITemplate(string: "https://api.github.com/repos/{"))
+        XCTAssertThrowsError(try URITemplate(string: "https://api.github.com/repos/{owner"))
+        XCTAssertThrowsError(try URITemplate(string: "https://api.github.com/repos/{owner,"))
+        XCTAssertThrowsError(try URITemplate(string: "https://api.github.com/repos/{owner*"))
+        XCTAssertThrowsError(try URITemplate(string: "https://api.github.com/repos/{owner:"))
+        XCTAssertThrowsError(try URITemplate(string: "https://api.github.com/repos/{owner:3"))
     }
 
     func testIncompletePercentEncodedTriplet() throws {