diff --git a/src/posix/cocoa/i_system.mm b/src/posix/cocoa/i_system.mm
index 712e9b7e4..f3eddd689 100644
--- a/src/posix/cocoa/i_system.mm
+++ b/src/posix/cocoa/i_system.mm
@@ -182,7 +182,7 @@ void I_Error (const char *error, ...)
 
 	va_start(argptr, error);
 
-	vsprintf (errortext, error, argptr);
+	myvsnprintf (errortext, MAX_ERRORTEXT, error, argptr);
 	va_end (argptr);
 	throw CRecoverableError(errortext);
 }
diff --git a/src/posix/sdl/i_system.cpp b/src/posix/sdl/i_system.cpp
index 16d3ee6d8..26f3519dd 100644
--- a/src/posix/sdl/i_system.cpp
+++ b/src/posix/sdl/i_system.cpp
@@ -243,7 +243,7 @@ void I_Error (const char *error, ...)
 
 	va_start(argptr, error);
 
-	vsprintf (errortext, error, argptr);
+	myvsnprintf (errortext, MAX_ERRORTEXT, error, argptr);
 	va_end (argptr);
 	throw CRecoverableError(errortext);
 }
diff --git a/src/sound/timidity/timidity.cpp b/src/sound/timidity/timidity.cpp
index e657466c0..a21596ade 100644
--- a/src/sound/timidity/timidity.cpp
+++ b/src/sound/timidity/timidity.cpp
@@ -827,7 +827,7 @@ void cmsg(int type, int verbosity_level, const char *fmt, ...)
 	char buf[1024];
 	va_list args;
 	va_start(args, fmt);
-	vsprintf(buf, fmt, args);
+	myvsnprintf(buf, sizeof buf, fmt, args);
 	va_end(args);
 	I_DebugPrint(buf);
 #endif
diff --git a/src/win32/i_crash.cpp b/src/win32/i_crash.cpp
index 86ae9cec9..4618762f8 100644
--- a/src/win32/i_crash.cpp
+++ b/src/win32/i_crash.cpp
@@ -501,7 +501,7 @@ void Writef (HANDLE file, const char *format, ...)
 	DWORD len;
 
 	va_start (args, format);
-	len = vsprintf (buffer, format, args);
+	len = myvsnprintf (buffer, sizeof buffer, format, args);
 	va_end (args);
 	WriteFile (file, buffer, len, &len, NULL);
 }