diff --git a/libs/isograph-react/src/core/cache.ts b/libs/isograph-react/src/core/cache.ts
index 956646ee..51f4dcc0 100644
--- a/libs/isograph-react/src/core/cache.ts
+++ b/libs/isograph-react/src/core/cache.ts
@@ -516,7 +516,7 @@ function normalizeLinkedField(
     const dataIds: (Link | null)[] = [];
     for (let i = 0; i < networkResponseData.length; i++) {
       const networkResponseObject = networkResponseData[i];
-      if (networkResponseObject === null) {
+      if (networkResponseObject == null) {
         dataIds.push(null);
         continue;
       }
diff --git a/libs/isograph-react/src/core/read.ts b/libs/isograph-react/src/core/read.ts
index b5152a42..60643ec7 100644
--- a/libs/isograph-react/src/core/read.ts
+++ b/libs/isograph-react/src/core/read.ts
@@ -342,10 +342,12 @@ function readData<TReadFromStore>(
           };
         } else {
           const refetchQueryIndex = field.refetchQuery;
-          if (refetchQueryIndex == null) {
-            throw new Error('refetchQuery is null in RefetchField');
-          }
           const refetchQuery = nestedRefetchQueries[refetchQueryIndex];
+          if (refetchQuery == null) {
+            throw new Error(
+              'refetchQuery is null in RefetchField. This is indicative of a bug in Isograph.',
+            );
+          }
           const refetchQueryArtifact = refetchQuery.artifact;
           const allowedVariables = refetchQuery.allowedVariables;
 
@@ -371,9 +373,15 @@ function readData<TReadFromStore>(
       }
       case 'Resolver': {
         const usedRefetchQueries = field.usedRefetchQueries;
-        const resolverRefetchQueries = usedRefetchQueries.map(
-          (index) => nestedRefetchQueries[index],
-        );
+        const resolverRefetchQueries = usedRefetchQueries.map((index) => {
+          const resolverRefetchQuery = nestedRefetchQueries[index];
+          if (resolverRefetchQuery == null) {
+            throw new Error(
+              'resolverRefetchQuery is null in Resolver. This is indicative of a bug in Isograph.',
+            );
+          }
+          return resolverRefetchQuery;
+        });
 
         switch (field.readerArtifact.kind) {
           case 'EagerReaderArtifact': {
@@ -636,7 +644,12 @@ function generateChildVariableMap(
   const childVars: Writable<Variables> = {};
   for (const [name, value] of fieldArguments) {
     if (value.kind === 'Variable') {
-      childVars[name] = variables[value.name];
+      const variable = variables[value.name];
+      // Variable could be null if it was not provided but has a default case,
+      // so we allow the loop to continue rather than throwing an error.
+      if (variable != null) {
+        childVars[name] = variable;
+      }
     } else {
       childVars[name] = value.value;
     }
diff --git a/libs/isograph-react/src/loadable-hooks/useConnectionSpecPagination.ts b/libs/isograph-react/src/loadable-hooks/useConnectionSpecPagination.ts
index 9c672369..7d39537e 100644
--- a/libs/isograph-react/src/loadable-hooks/useConnectionSpecPagination.ts
+++ b/libs/isograph-react/src/loadable-hooks/useConnectionSpecPagination.ts
@@ -114,8 +114,16 @@ export function useConnectionSpecPagination<
         fragmentReference.readerWithRefetchQueries,
       );
 
+      // invariant: readOutDataAndRecords.length === completedReferences.length
+      const data = readOutDataAndRecords[i]?.item;
+      if (data == null) {
+        throw new Error(
+          'Parameter data is unexpectedly null. This is indicative of a bug in Isograph.',
+        );
+      }
+
       const firstParameter = {
-        data: readOutDataAndRecords[i].item,
+        data,
         parameters: fragmentReference.variables,
       };
 
@@ -165,10 +173,17 @@ export function useConnectionSpecPagination<
           fragmentReference.readerWithRefetchQueries,
         );
 
+        const records = readOutDataAndRecords[i];
+        if (records == null) {
+          throw new Error(
+            'subscribeCompletedFragmentReferences records is unexpectedly null',
+          );
+        }
+
         return {
           fragmentReference,
           readerAst: readerWithRefetchQueries.readerArtifact.readerAst,
-          records: readOutDataAndRecords[i],
+          records,
           callback(_data) {
             rerender({});
           },
@@ -224,10 +239,9 @@ export function useConnectionSpecPagination<
 
   const loadedReferences = state === UNASSIGNED_STATE ? [] : state;
 
-  const mostRecentItem: LoadedFragmentReference<
-    TReadFromStore,
-    Connection<TItem>
-  > | null = loadedReferences[loadedReferences.length - 1];
+  const mostRecentItem:
+    | LoadedFragmentReference<TReadFromStore, Connection<TItem>>
+    | undefined = loadedReferences[loadedReferences.length - 1];
   const mostRecentFragmentReference =
     mostRecentItem?.[0].getItemIfNotDisposed();
 
diff --git a/libs/isograph-react/src/loadable-hooks/useSkipLimitPagination.ts b/libs/isograph-react/src/loadable-hooks/useSkipLimitPagination.ts
index 46a077fb..07d29a9a 100644
--- a/libs/isograph-react/src/loadable-hooks/useSkipLimitPagination.ts
+++ b/libs/isograph-react/src/loadable-hooks/useSkipLimitPagination.ts
@@ -106,8 +106,16 @@ export function useSkipLimitPagination<
         fragmentReference.readerWithRefetchQueries,
       );
 
+      // invariant: readOutDataAndRecords.length === completedReferences.length
+      const data = readOutDataAndRecords[i]?.item;
+      if (data == null) {
+        throw new Error(
+          'Parameter data is unexpectedly null. This is indicative of a bug in Isograph.',
+        );
+      }
+
       const firstParameter = {
-        data: readOutDataAndRecords[i].item,
+        data,
         parameters: fragmentReference.variables,
       };
 
@@ -150,10 +158,17 @@ export function useSkipLimitPagination<
           fragmentReference.readerWithRefetchQueries,
         );
 
+        const records = readOutDataAndRecords[i];
+        if (records == null) {
+          throw new Error(
+            'subscribeCompletedFragmentReferences records is unexpectedly null',
+          );
+        }
+
         return {
           fragmentReference,
           readerAst: readerWithRefetchQueries.readerArtifact.readerAst,
-          records: readOutDataAndRecords[i],
+          records,
           callback(_data) {
             rerender({});
           },
@@ -209,8 +224,9 @@ export function useSkipLimitPagination<
 
   const loadedReferences = state === UNASSIGNED_STATE ? [] : state;
 
-  const mostRecentItem: LoadedFragmentReference<TReadFromStore, TItem> | null =
-    loadedReferences[loadedReferences.length - 1];
+  const mostRecentItem:
+    | LoadedFragmentReference<TReadFromStore, TItem>
+    | undefined = loadedReferences[loadedReferences.length - 1];
   const mostRecentFragmentReference =
     mostRecentItem?.[0].getItemIfNotDisposed();
 
diff --git a/tsconfig.build.json b/tsconfig.build.json
index 288b569d..3769b86f 100644
--- a/tsconfig.build.json
+++ b/tsconfig.build.json
@@ -15,6 +15,7 @@
     "noPropertyAccessFromIndexSignature": true,
     "noUnusedParameters": true,
     "exactOptionalPropertyTypes": true,
+    "noUncheckedIndexedAccess": true,
     "paths": {
       "@isograph/*": ["./libs/*"]
     },