diff --git a/Bugsnag/KSCrash/Source/KSCrash/Recording/Tools/BSG_KSJSONCodecObjC.m b/Bugsnag/KSCrash/Source/KSCrash/Recording/Tools/BSG_KSJSONCodecObjC.m
index b18e19572..b687d6e30 100644
--- a/Bugsnag/KSCrash/Source/KSCrash/Recording/Tools/BSG_KSJSONCodecObjC.m
+++ b/Bugsnag/KSCrash/Source/KSCrash/Recording/Tools/BSG_KSJSONCodecObjC.m
@@ -447,10 +447,12 @@ int bsg_ksjsoncodecobjc_i_encodeObject(BSG_KSJSONCodec *codec, id object,
             keys = [keys sortedArrayUsingSelector:@selector(compare:)];
         }
         for (id key in keys) {
-            if ((result = bsg_ksjsoncodecobjc_i_encodeObject(
-                     codec, [object valueForKey:key], key, context)) !=
-                BSG_KSJSON_OK) {
-                return result;
+            if([key isKindOfClass:[NSString class]]) {
+                if ((result = bsg_ksjsoncodecobjc_i_encodeObject(
+                         codec, [object valueForKey:key], key, context)) !=
+                    BSG_KSJSON_OK) {
+                    return result;
+                }
             }
         }
         return bsg_ksjsonendContainer(context);
diff --git a/CHANGELOG.md b/CHANGELOG.md
index f526c4f23..0967093d4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,13 @@
 Changelog
 =========
 
+## TBD
+
+### Bug fixes
+
+* Guard against non-string metadata map keys
+  [#790](https://bugsnag.atlassian.net/browse/PLAT-4685)
+
 ## 6.1.3 (2020-08-17)
 
 ### Bug fixes
diff --git a/Tests/BugsnagClientTests.m b/Tests/BugsnagClientTests.m
index b92be7594..e26b1e515 100644
--- a/Tests/BugsnagClientTests.m
+++ b/Tests/BugsnagClientTests.m
@@ -278,6 +278,27 @@ - (void)testLargeBreadcrumbSize {
     XCTAssertEqualObjects(largeMetadata, crumb.metadata);
 }
 
+- (void)testMetadataInvalidKey {
+    BugsnagConfiguration *configuration = [[BugsnagConfiguration alloc] initWithApiKey:DUMMY_APIKEY_32CHAR_1];
+    configuration.enabledBreadcrumbTypes = BSGEnabledBreadcrumbTypeNone;
+    BugsnagClient *client = [[BugsnagClient alloc] initWithConfiguration:configuration];
+    [client start];
+
+    NSMutableArray *breadcrumbs = client.breadcrumbs.breadcrumbs;
+    XCTAssertEqual(0, [breadcrumbs count]);
+
+    id badMetadata = @{
+        @"test": @"string key is fine",
+        @85 : @"numeric key would break JSON"
+    };
+
+    [client leaveBreadcrumbWithMessage:@"test msg" metadata:badMetadata andType:BSGBreadcrumbTypeUser];
+
+    XCTAssertEqual(1, [breadcrumbs count]);
+
+    [client notifyError:[NSError errorWithDomain:@"test" code:0 userInfo:badMetadata]];
+}
+
 - (NSDictionary *)generateLargeMetadata {
     NSMutableDictionary *dict = [NSMutableDictionary new];