diff --git a/common/init.c b/common/init.c
index 6ea9ea5c..03124b30 100644
--- a/common/init.c
+++ b/common/init.c
@@ -9,7 +9,7 @@
 #include "ui.h"
 #include "uipriv.h"
 
-static int initialized = 0;
+static bool initialized = false;
 
 #define errAlreadyInitialized "libui already initialized"
 #define errOptionsMustBeNULL "options parameter to uiInit() must be NULL"
@@ -20,33 +20,33 @@ static const char *commonInitErrors[] = {
 	NULL,
 };
 
-static int checkInitErrorLengths(uiInitError *err, const char **initErrors)
+static bool checkInitErrorLengths(uiInitError *err, const char **initErrors)
 {
 	const char **p;
 
 	if (initErrors == NULL)
-		return 1;
+		return true;
 	for (p = initErrors; *p != NULL; p++)
 		if (strlen(*p) > 255) {
 			strcpy(err->Message, "[INTERNAL] uiInit() error too long: ");
 			strncat(err->Message, *p, 32);
 			strcat(err->Message, "...");
-			return 0;
+			return false;
 		}
-	return 1;
+	return true;
 }
 
-int uiInit(void *options, uiInitError *err)
+bool uiInit(void *options, uiInitError *err)
 {
 	if (err == NULL)
-		return 0;
+		return false;
 	if (err->Size != sizeof (uiInitError))
-		return 0;
+		return false;
 
 	if (!checkInitErrorLengths(err, commonInitErrors))
-		return 0;
+		return false;
 	if (!checkInitErrorLengths(err, uiprivSysInitErrors()))
-		return 0;
+		return false;
 
 	if (initialized)
 		return uiprivInitReturnError(err, errAlreadyInitialized);
@@ -55,19 +55,19 @@ int uiInit(void *options, uiInitError *err)
 		return uiprivInitReturnError(err, errOptionsMustBeNULL);
 
 	if (!uiprivSysInit(options, err))
-		return 0;
-	initialized = 1;
-	return 1;
+		return false;
+	initialized = true;
+	return true;
 }
 
-int uiprivInitReturnError(uiInitError *err, const char *msg)
+bool uiprivInitReturnError(uiInitError *err, const char *msg)
 {
 	// checkInitErrorLengths() above ensures that err->Message[255] will always be '\0'
 	strncpy(err->Message, msg, 256);
-	return 0;
+	return false;
 }
 
-int uiprivInitReturnErrorf(uiInitError *err, const char *msg, ...)
+bool uiprivInitReturnErrorf(uiInitError *err, const char *msg, ...)
 {
 	va_list ap;
 
@@ -75,7 +75,7 @@ int uiprivInitReturnErrorf(uiInitError *err, const char *msg, ...)
 	va_start(ap, msg);
 	vsnprintf(err->Message, 256, msg, ap);
 	va_end(ap);
-	return 0;
+	return false;
 }
 
 bool uiprivCheckInitializedAndThreadImpl(const char *func)
diff --git a/common/uipriv.h b/common/uipriv.h
index befbbeac..bfd474fa 100644
--- a/common/uipriv.h
+++ b/common/uipriv.h
@@ -21,9 +21,9 @@ extern "C" {
 
 // init.c
 extern const char **uiprivSysInitErrors(void);
-extern int uiprivSysInit(void *options, uiInitError *err);
-extern int uiprivInitReturnError(uiInitError *err, const char *msg);
-extern int uiprivInitReturnErrorf(uiInitError *err, const char *msg, ...);
+extern bool uiprivSysInit(void *options, uiInitError *err);
+extern bool uiprivInitReturnError(uiInitError *err, const char *msg);
+extern bool uiprivInitReturnErrorf(uiInitError *err, const char *msg, ...);
 extern bool uiprivCheckInitializedAndThreadImpl(const char *func);
 #define uiprivCheckInitializedAndThread() uiprivCheckInitializedAndThreadImpl(uiprivFunc)
 extern bool uiprivSysCheckThread(void);
diff --git a/darwin/main.m b/darwin/main.m
index 9b6010b0..f1f44ae6 100644
--- a/darwin/main.m
+++ b/darwin/main.m
@@ -51,7 +51,7 @@ const char **uiprivSysInitErrors(void)
 static pthread_t mainThread;
 static BOOL initialized = NO;		// TODO deduplicate this from common/init.c
 
-int uiprivSysInit(void *options, uiInitError *err)
+bool uiprivSysInit(void *options, uiInitError *err)
 {
 	uiprivApp = [uiprivApplication sharedApplication];
 	if (![NSApp isKindOfClass:[uiprivApplication class]])
@@ -66,7 +66,7 @@ int uiprivSysInit(void *options, uiInitError *err)
 
 	mainThread = pthread_self();
 	initialized = YES;
-	return 1;
+	return true;
 }
 
 void uiMain(void)
diff --git a/doc/init-main.md b/doc/init-main.md
index bd907c0c..baef6032 100644
--- a/doc/init-main.md
+++ b/doc/init-main.md
@@ -78,10 +78,10 @@ TODO timers
 ### `uiInit()`
 
 ```c
-int uiInit(void *options, uiInitError *err);
+bool uiInit(void *options, uiInitError *err);
 ```
 
-`uiInit()` initializes libui. It returns nonzero on success and zero on failure; in the event of a failure, `err` is filled with relevant information explaining the failure.
+`uiInit()` initializes libui. It returns `true` on success and `false` on failure; in the event of a failure, `err` is filled with relevant information explaining the failure.
 
 `err` is required and must be properly initialized. If `err` is `NULL` or `err->Size` does not match `sizeof (uiError)`, `uiInit()` immediately returns zero without doing anything. If any of the other fields of `err` are not zero-initialized as with `memset(0)`, the behavior is undefined.
 
diff --git a/ui.h b/ui.h
index 82a1570b..161a783b 100644
--- a/ui.h
+++ b/ui.h
@@ -38,7 +38,7 @@ struct uiInitError {
 	char Message[256];
 };
 
-uiprivExtern int uiInit(void *options, uiInitError *err);
+uiprivExtern bool uiInit(void *options, uiInitError *err);
 uiprivExtern void uiMain(void);
 uiprivExtern void uiQuit(void);
 uiprivExtern void uiQueueMain(void (*f)(void *data), void *data);
diff --git a/unix/main.c b/unix/main.c
index 8e49281b..dda450aa 100644
--- a/unix/main.c
+++ b/unix/main.c
@@ -9,7 +9,7 @@ const char **uiprivSysInitErrors(void)
 static pthread_t mainThread;
 static gboolean initialized = FALSE;		// TODO deduplicate this from common/init.c
 
-int uiprivSysInit(void *options, uiInitError *err)
+bool uiprivSysInit(void *options, uiInitError *err)
 {
 	GError *gerr = NULL;
 
@@ -17,11 +17,11 @@ int uiprivSysInit(void *options, uiInitError *err)
 		// TODO make sure this is safe
 		strncpy(err->Message, gerr->message, 255);
 		g_error_free(gerr);
-		return 0;
+		return false;
 	}
 	mainThread = pthread_self();
 	initialized = TRUE;
-	return 1;
+	return true;
 }
 
 void uiMain(void)
diff --git a/windows/main.cpp b/windows/main.cpp
index dff287c0..58150aca 100644
--- a/windows/main.cpp
+++ b/windows/main.cpp
@@ -69,7 +69,7 @@ const char **uiprivSysInitErrors(void)
 static DWORD mainThread;
 static BOOL initialized = FALSE;		// TODO deduplicate this from common/init.c
 
-int uiprivSysInit(void *options, uiInitError *err)
+bool uiprivSysInit(void *options, uiInitError *err)
 {
 	STARTUPINFOW si;
 	HICON hDefaultIcon;
@@ -115,7 +115,7 @@ int uiprivSysInit(void *options, uiInitError *err)
 */
 	mainThread = GetCurrentThreadId();
 	initialized = TRUE;
-	return 1;
+	return true;
 }
 
 void uiMain(void)