diff --git a/src/LaunchDarkly.OpenFeature.ServerProvider/EvalContextConverter.cs b/src/LaunchDarkly.OpenFeature.ServerProvider/EvalContextConverter.cs
index 210dc7a..b361cab 100644
--- a/src/LaunchDarkly.OpenFeature.ServerProvider/EvalContextConverter.cs
+++ b/src/LaunchDarkly.OpenFeature.ServerProvider/EvalContextConverter.cs
@@ -33,6 +33,14 @@ public EvalContextConverter(Logger log)
         private static string InvalidTypeMessage(string attribute, string type) => $"The attribute '{attribute}' " +
             $"must be of type {type}";
 
+        /// <summary>
+        /// Get the value as a string, or null if it is not a string or is empty.
+        /// </summary>
+        /// <param name="value">The value to inspect</param>
+        /// <returns>The non-empty string value, or null</returns>
+        private static string NonEmptyString(Value value) =>
+            value != null && value.IsString && value.AsString.Length != 0 ? value.AsString : null;
+
         /// <summary>
         /// Extract a string value and log an error if the value was not a string.
         /// </summary>
@@ -196,10 +204,17 @@ private Context BuildSingleLdContext(IImmutableDictionary<string, Value> attribu
         {
             // targetingKey is in the specification, so it takes precedence.
             attributes.TryGetValue("key", out var keyAttr);
-            attributes.TryGetValue("targetingKey", out var targetingKey);
-            var finalKey = (targetingKey ?? keyAttr)?.AsString;
+            attributes.TryGetValue("targetingKey", out var targetingKeyAttr);
+            var targetingKey = NonEmptyString(targetingKeyAttr);
+            var keyFromAttr = NonEmptyString(keyAttr);
+            var finalKey = targetingKey ?? keyFromAttr;
+
+            if (keyAttr != null && !keyAttr.IsNull && !keyAttr.IsString)
+            {
+                _log.Warn("A non-string 'key' attribute was provided.");
+            }
 
-            if (keyAttr != null && targetingKey != null)
+            if (keyFromAttr != null && targetingKey != null)
             {
                 _log.Warn("The EvaluationContext contained both a 'targetingKey' and a 'key' attribute. The 'key'" +
                           " attribute will be discarded.");
diff --git a/test/LaunchDarkly.OpenFeature.ServerProvider.Tests/EvalContextConverterTests.cs b/test/LaunchDarkly.OpenFeature.ServerProvider.Tests/EvalContextConverterTests.cs
index 01b8478..fdc2025 100644
--- a/test/LaunchDarkly.OpenFeature.ServerProvider.Tests/EvalContextConverterTests.cs
+++ b/test/LaunchDarkly.OpenFeature.ServerProvider.Tests/EvalContextConverterTests.cs
@@ -179,6 +179,46 @@ public void ItUsesTheTargetingKeyInFavorOfKey()
             Assert.Equal("targeting-key", _converter.ToLdContext(evaluationContext).Key);
         }
 
+        [Fact]
+        public void ItIgnoresANonStringKey()
+        {
+            var evaluationContext = EvaluationContext.Builder()
+                .Set("key", 42)
+                .Build();
+
+            Assert.False(_converter.ToLdContext(evaluationContext).Valid);
+            Assert.True(_logCapture.HasMessageWithText(LogLevel.Warn,
+                "A non-string 'key' attribute was provided."));
+            Assert.True(_logCapture.HasMessageWithText(LogLevel.Error,
+                "The EvaluationContext must contain either a 'targetingKey' or a 'key' and the type" +
+                " must be a string."));
+        }
+
+        [Fact]
+        public void ItUsesTheKeyAttributeWhenTheTargetingKeyIsEmpty()
+        {
+            var evaluationContext = EvaluationContext.Builder()
+                .Set("targetingKey", "")
+                .Set("key", "the-key")
+                .Build();
+
+            Assert.Equal("the-key", _converter.ToLdContext(evaluationContext).Key);
+            Assert.Empty(_logCapture.GetMessages());
+        }
+
+        [Fact]
+        public void ItLogsAnErrorWhenTheOnlyKeyIsEmpty()
+        {
+            var evaluationContext = EvaluationContext.Builder()
+                .Set("targetingKey", "")
+                .Build();
+
+            Assert.False(_converter.ToLdContext(evaluationContext).Valid);
+            Assert.True(_logCapture.HasMessageWithText(LogLevel.Error,
+                "The EvaluationContext must contain either a 'targetingKey' or a 'key' and the type" +
+                " must be a string."));
+        }
+
         [Fact]
         public void ItCanBuildASingleContext()
         {