diff --git a/api/adapter.c b/api/adapter.c
index 63e1e76..e229249 100644
--- a/api/adapter.c
+++ b/api/adapter.c
@@ -287,7 +287,7 @@ AdapterEnableAll(_In_ HDEVINFO DevInfo, _In_ SP_DEVINFO_DATA_LIST *AdaptersToEna
 }
 
 WINTUN_STATUS
-AdapterDeleteAllOurs()
+AdapterDeleteAllOurs(void)
 {
     DWORD Result = ERROR_SUCCESS;
     HDEVINFO DevInfo = SetupDiGetClassDevsExW(&GUID_DEVCLASS_NET, NULL, NULL, DIGCF_PRESENT, NULL, NULL, NULL);
@@ -328,7 +328,7 @@ AdapterDeleteAllOurs()
 }
 
 void
-AdapterInit()
+AdapterInit(void)
 {
     Locale = _wcreate_locale(LC_ALL, L"");
 
@@ -350,7 +350,7 @@ AdapterInit()
 }
 
 void
-AdapterCleanup()
+AdapterCleanup(void)
 {
     _free_locale(Locale);
 }
@@ -791,7 +791,7 @@ extern VOID NTAPI
 RtlGetNtVersionNumbers(_Out_opt_ DWORD *MajorVersion, _Out_opt_ DWORD *MinorVersion, _Out_opt_ DWORD *BuildNumber);
 
 static BOOL
-HaveWHQL()
+HaveWHQL(void)
 {
 #    if defined(HAVE_EV) && defined(HAVE_WHQL)
     DWORD MajorVersion;
diff --git a/api/adapter.h b/api/adapter.h
index 5b9b651..04a9983 100644
--- a/api/adapter.h
+++ b/api/adapter.h
@@ -70,13 +70,13 @@ AdapterEnableAll(_In_ HDEVINFO DevInfo, _In_ SP_DEVINFO_DATA_LIST *AdaptersToEna
  * @return ERROR_SUCCESS on success; Win32 error code otherwise.
  */
 WINTUN_STATUS
-AdapterDeleteAllOurs();
+AdapterDeleteAllOurs(void);
 
 void
-AdapterInit();
+AdapterInit(void);
 
 void
-AdapterCleanup();
+AdapterCleanup(void);
 
 /**
  * Wintun adapter descriptor.
diff --git a/api/namespace.c b/api/namespace.c
index 8c4d4bc..2daf2f3 100644
--- a/api/namespace.c
+++ b/api/namespace.c
@@ -41,7 +41,7 @@ Bin2Hex(_In_bytecount_(Size) const void *Source, size_t Size, _Out_capcount_(Siz
 }
 
 static WINTUN_STATUS
-NamespaceRuntimeInit()
+NamespaceRuntimeInit(void)
 {
     DWORD Result;
 
@@ -165,13 +165,13 @@ NamespaceReleaseMutex(_In_ HANDLE Mutex)
 }
 
 void
-NamespaceInit()
+NamespaceInit(void)
 {
     InitializeCriticalSection(&Initializing);
 }
 
 void
-NamespaceCleanup()
+NamespaceCleanup(void)
 {
     EnterCriticalSection(&Initializing);
     if (HasInitialized)
diff --git a/api/namespace.h b/api/namespace.h
index 8a26c4b..753068d 100644
--- a/api/namespace.h
+++ b/api/namespace.h
@@ -15,7 +15,7 @@ void
 NamespaceReleaseMutex(_In_ HANDLE Mutex);
 
 void
-NamespaceInit();
+NamespaceInit(void);
 
 void
-NamespaceCleanup();
+NamespaceCleanup(void);
diff --git a/api/nci.c b/api/nci.c
index 40c9edc..f57423d 100644
--- a/api/nci.c
+++ b/api/nci.c
@@ -16,7 +16,7 @@ DWORD(WINAPI *NciGetConnectionName)
  _Out_opt_ DWORD *OutDestNameBytes);
 
 void
-NciInit()
+NciInit(void)
 {
     NciModule = LoadLibraryW(L"nci.dll");
     if (!NciModule)
@@ -28,7 +28,7 @@ NciInit()
 }
 
 void
-NciCleanup()
+NciCleanup(void)
 {
     if (NciModule)
         FreeLibrary(NciModule);
diff --git a/api/nci.h b/api/nci.h
index 5090c90..4288655 100644
--- a/api/nci.h
+++ b/api/nci.h
@@ -16,7 +16,7 @@ extern DWORD(WINAPI *NciGetConnectionName)(
     _Out_opt_ DWORD *OutDestNameBytes);
 
 void
-NciInit();
+NciInit(void);
 
 void
-NciCleanup();
+NciCleanup(void);