diff --git a/include/efiauthenticated.h b/include/efiauthenticated.h
index a9c395f..7157ffd 100644
--- a/include/efiauthenticated.h
+++ b/include/efiauthenticated.h
@@ -119,8 +119,6 @@ typedef struct {
 	//UINT8 Signature[];
 } WIN_CERTIFICATE_EFI_PKCS1_15;
 
-#define OFFSET_OF(TYPE, Field) ((UINTN) &(((TYPE *)0)->Field))
-
 /*
  * Attributes of Authenticated Variable
  */
@@ -182,14 +180,14 @@ typedef struct {
 /*
  * Size of AuthInfo prior to the data payload.
  */
-#define AUTHINFO_SIZE ((OFFSET_OF (EFI_VARIABLE_AUTHENTICATION, AuthInfo)) + \
-                       (OFFSET_OF (WIN_CERTIFICATE_UEFI_GUID, CertData)) + \
+#define AUTHINFO_SIZE ((offsetof(EFI_VARIABLE_AUTHENTICATION, AuthInfo)) + \
+                       (offsetof(WIN_CERTIFICATE_UEFI_GUID, CertData)) + \
                        sizeof (EFI_CERT_BLOCK_RSA_2048_SHA256))
 
-#define AUTHINFO2_SIZE(VarAuth2) ((OFFSET_OF (EFI_VARIABLE_AUTHENTICATION_2, AuthInfo)) + \
+#define AUTHINFO2_SIZE(VarAuth2) ((offsetof(EFI_VARIABLE_AUTHENTICATION_2, AuthInfo)) + \
                                   (UINTN) ((EFI_VARIABLE_AUTHENTICATION_2 *) (VarAuth2))->AuthInfo.Hdr.dwLength)
 
-#define OFFSET_OF_AUTHINFO2_CERT_DATA ((OFFSET_OF (EFI_VARIABLE_AUTHENTICATION_2, AuthInfo)) + \
-                                       (OFFSET_OF (WIN_CERTIFICATE_UEFI_GUID, CertData)))
+#define OFFSET_OF_AUTHINFO2_CERT_DATA ((offsetof(EFI_VARIABLE_AUTHENTICATION_2, AuthInfo)) + \
+                                       (offsetof(WIN_CERTIFICATE_UEFI_GUID, CertData)))
 
 #endif /* SHIM_EFIAUTHENTICATED_H */
diff --git a/lib/simple_file.c b/lib/simple_file.c
index 2b82313..b9bafd3 100644
--- a/lib/simple_file.c
+++ b/lib/simple_file.c
@@ -314,7 +314,7 @@ simple_dir_filter(EFI_HANDLE image, CHAR16 *name, CHAR16 *filter,
 				break;
 			}
 		}
-		ptr += OFFSET_OF(EFI_FILE_INFO, FileName) + (len + 1)*sizeof(CHAR16);
+		ptr += offsetof(EFI_FILE_INFO, FileName) + (len + 1)*sizeof(CHAR16);
 		next = ptr;
 	}
 	if (*count)
@@ -367,7 +367,7 @@ simple_dir_filter(EFI_HANDLE image, CHAR16 *name, CHAR16 *filter,
 			(*result)[0] = tmp;
 		}
 
-		ptr += OFFSET_OF(EFI_FILE_INFO, FileName) + (len + 1)*sizeof(CHAR16);
+		ptr += offsetof(EFI_FILE_INFO, FileName) + (len + 1)*sizeof(CHAR16);
 		next = ptr;
 	}
 	if (*count == 0) {
diff --git a/lib/variables.c b/lib/variables.c
index 0abd6a0..044ddae 100644
--- a/lib/variables.c
+++ b/lib/variables.c
@@ -74,10 +74,8 @@ CreateTimeBasedPayload(IN OUT UINTN * DataSize, IN OUT UINT8 ** Data)
 	Payload = *Data;
 	PayloadSize = *DataSize;
 
-	DescriptorSize =
-	    OFFSET_OF(EFI_VARIABLE_AUTHENTICATION_2,
-		      AuthInfo) + OFFSET_OF(WIN_CERTIFICATE_UEFI_GUID,
-					    CertData);
+	DescriptorSize = offsetof(EFI_VARIABLE_AUTHENTICATION_2, AuthInfo)
+			+ offsetof(WIN_CERTIFICATE_UEFI_GUID, CertData);
 	NewData = (UINT8 *) AllocateZeroPool(DescriptorSize + PayloadSize);
 	if (NewData == NULL) {
 		return EFI_OUT_OF_RESOURCES;
@@ -103,7 +101,7 @@ CreateTimeBasedPayload(IN OUT UINTN * DataSize, IN OUT UINT8 ** Data)
 	CopyMem(&DescriptorData->TimeStamp, &Time, sizeof(EFI_TIME));
 
 	DescriptorData->AuthInfo.Hdr.dwLength =
-	    OFFSET_OF(WIN_CERTIFICATE_UEFI_GUID, CertData);
+		offsetof(WIN_CERTIFICATE_UEFI_GUID, CertData);
 	DescriptorData->AuthInfo.Hdr.wRevision = 0x0200;
 	DescriptorData->AuthInfo.Hdr.wCertificateType = WIN_CERT_TYPE_EFI_GUID;
 	DescriptorData->AuthInfo.CertType = EFI_CERT_TYPE_PKCS7_GUID;
diff --git a/shim.h b/shim.h
index 89d2432..70fdf77 100644
--- a/shim.h
+++ b/shim.h
@@ -4,6 +4,8 @@
 #include <efi.h>
 #include <efilib.h>
 
+#include <stddef.h>
+
 #define min(a, b) ({(a) < (b) ? (a) : (b);})
 
 #ifdef __x86_64__