diff --git a/src/compiler/commandLineParser.ts b/src/compiler/commandLineParser.ts
index c8e6353da08..e00d47d1a66 100644
--- a/src/compiler/commandLineParser.ts
+++ b/src/compiler/commandLineParser.ts
@@ -1633,7 +1633,7 @@ namespace ts {
             text = readFile(fileName);
         }
         catch (e) {
-            return createCompilerDiagnostic(Diagnostics.Cannot_read_file_0_Colon_1, fileName, e.message);
+            return createCompilerDiagnostic(Diagnostics.Cannot_read_file_0_Colon_1, fileName, (e as Error).message);
         }
         return text === undefined ? createCompilerDiagnostic(Diagnostics.Cannot_read_file_0, fileName) : text;
     }
diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index 8d4efc3e941..0fad9661fb5 100644
--- a/src/compiler/program.ts
+++ b/src/compiler/program.ts
@@ -83,7 +83,7 @@ namespace ts {
                 performance.measure("I/O Read", "beforeIORead", "afterIORead");
             }
             catch (e) {
-                if (onError) {
+                if (onError && e instanceof Error) {
                     onError(e.message);
                 }
                 text = "";
@@ -121,7 +121,7 @@ namespace ts {
                 performance.measure("I/O Write", "beforeIOWrite", "afterIOWrite");
             }
             catch (e) {
-                if (onError) {
+                if (onError && e instanceof Error) {
                     onError(e.message);
                 }
             }
diff --git a/src/compiler/sys.ts b/src/compiler/sys.ts
index 0b3080138d6..53bd670c4f6 100644
--- a/src/compiler/sys.ts
+++ b/src/compiler/sys.ts
@@ -1242,7 +1242,7 @@ namespace ts {
                             _fs.mkdirSync(directoryName);
                         }
                         catch (e) {
-                            if (e.code !== "EEXIST") {
+                            if ((e as {code: string}).code !== "EEXIST") {
                                 // Failed for some other reason (access denied?); still throw
                                 throw e;
                             }
@@ -1312,7 +1312,7 @@ namespace ts {
                         const modulePath = resolveJSModule(moduleName, baseDir, nodeSystem);
                         return { module: require(modulePath), modulePath, error: undefined };
                     }
-                    catch (error) {
+                    catch (error: any) {
                         return { module: undefined, modulePath: undefined, error };
                     }
                 }
diff --git a/src/compiler/watch.ts b/src/compiler/watch.ts
index ab7c06ee482..3e4e6439af7 100644
--- a/src/compiler/watch.ts
+++ b/src/compiler/watch.ts
@@ -291,7 +291,7 @@ namespace ts {
                     performance.measure("I/O Read", "beforeIORead", "afterIORead");
                 }
                 catch (e) {
-                    if (onError) {
+                    if (onError && e instanceof Error) {
                         onError(e.message);
                     }
                     text = "";
@@ -317,7 +317,7 @@ namespace ts {
             readDirectory: maybeBind(host, host.readDirectory),
         };
 
-        function writeFile(fileName: string, text: string, writeByteOrderMark: boolean, onError: (message: string) => void) {
+        function writeFile(fileName: string, text: string, writeByteOrderMark: boolean, onError?: (message: string) => void) {
             try {
                 performance.mark("beforeIOWrite");
 
@@ -336,7 +336,7 @@ namespace ts {
                 performance.measure("I/O Write", "beforeIOWrite", "afterIOWrite");
             }
             catch (e) {
-                if (onError) {
+                if (onError && e instanceof Error) {
                     onError(e.message);
                 }
             }
diff --git a/src/services/shims.ts b/src/services/shims.ts
index 14f6a61e747..97143fa22a7 100644
--- a/src/services/shims.ts
+++ b/src/services/shims.ts
@@ -451,7 +451,7 @@ namespace ts {
                 return JSON.parse(diagnosticMessagesJson);
             }
             catch (e) {
-                this.log(e.description || "diagnosticMessages.generated.json has invalid JSON format");
+                this.log((e as { description?: string }).description || "diagnosticMessages.generated.json has invalid JSON format");
                 return null;
             }
             /* eslint-enable no-null/no-null */
@@ -579,7 +579,7 @@ namespace ts {
             const result = simpleForwardCall(logger, actionDescription, action, logPerformance);
             return returnJson ? JSON.stringify({ result }) : result as T;
         }
-        catch (err) {
+        catch (err: any) {
             if (err instanceof OperationCanceledException) {
                 return JSON.stringify({ canceled: true });
             }
@@ -1283,7 +1283,7 @@ namespace ts {
                 const languageService = createLanguageService(hostAdapter, this.documentRegistry, /*syntaxOnly*/ false);
                 return new LanguageServiceShimObject(this, host, languageService);
             }
-            catch (err) {
+            catch (err: any) {
                 logInternalError(host, err);
                 throw err;
             }
@@ -1293,7 +1293,7 @@ namespace ts {
             try {
                 return new ClassifierShimObject(this, logger);
             }
-            catch (err) {
+            catch (err: any) {
                 logInternalError(logger, err);
                 throw err;
             }
@@ -1304,7 +1304,7 @@ namespace ts {
                 const adapter = new CoreServicesShimHostAdapter(host);
                 return new CoreServicesShimObject(this, <Logger>host, adapter);
             }
-            catch (err) {
+            catch (err: any) {
                 logInternalError(<Logger>host, err);
                 throw err;
             }