diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 3dd24908..61cd1f55 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -222,8 +222,17 @@ target_include_directories(jopa PRIVATE
     "${CMAKE_CURRENT_SOURCE_DIR}/codegen"
     "${CMAKE_BINARY_DIR}/generated"
 )
+# Silence third-party header warnings.
+if(LIBZIP_INCLUDE_DIRS)
+    target_include_directories(jopa SYSTEM PRIVATE ${LIBZIP_INCLUDE_DIRS})
+endif()
 target_link_libraries(jopa PRIVATE ${JOPA_LIBS})
 
+# Suppress nullability extension noise from libzip headers when using Clang.
+if(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
+    target_compile_options(jopa PRIVATE -Wno-nullability-extension)
+endif()
+
 # Depend on grammar generation if available
 if(TARGET generate_parser)
     add_dependencies(jopa generate_parser)
diff --git a/src/error.cpp b/src/error.cpp
index 3000ac04..96eba162 100644
--- a/src/error.cpp
+++ b/src/error.cpp
@@ -112,7 +112,7 @@ ErrorString& ErrorString::operator<<(const char* s)
 ErrorString& ErrorString::operator<<(int n)
 {
     char buf[64];
-    sprintf(buf, "%d", n);
+    snprintf(buf, sizeof(buf), "%d", n);
 
     return (*this << buf);
 }
diff --git a/src/platform.h b/src/platform.h
index 5f4e9ff5..5b27c89c 100644
--- a/src/platform.h
+++ b/src/platform.h
@@ -98,15 +98,15 @@
 # include STD_LIB_NAME(errno)
 #endif
 
-#ifndef HAVE_WINT_T
-/* On some systems the type wint_t is not defined in wchar.h */
-typedef unsigned int wint_t;
-#endif
-
 #ifdef HAVE_WCHAR_H
 # include STD_LIB_NAME(wchar)
 #endif
 
+#if !defined(HAVE_WINT_T) && !defined(_WINT_T)
+/* On some systems the type wint_t is not defined in wchar.h */
+typedef unsigned int wint_t;
+#endif
+
 #ifdef HAVE_CTYPE_H
 # include STD_LIB_NAME(ctype)
 #endif
diff --git a/src/symbol.cpp b/src/symbol.cpp
index f6f26430..1205d702 100644
--- a/src/symbol.cpp
+++ b/src/symbol.cpp
@@ -1037,8 +1037,8 @@ void DirectorySymbol::ReadDirectory()
                 {
                     int len = DirectoryNameLength() + strlen(entry -> d_name);
                     char* filename = new char[len + 2]; // +2 for '/', NUL
-                    sprintf(filename, "%s/%s", DirectoryName(),
-                            entry -> d_name);
+                    snprintf(filename, len + 2, "%s/%s", DirectoryName(),
+                             entry -> d_name);
                     struct stat status;
                     if(JopaAPI::getInstance() -> stat(filename, &status) == 0)
                         entries -> InsertEntry(this, entry -> d_name, length);
diff --git a/src/zipfile.h b/src/zipfile.h
index ee9ae686..c6464b92 100644
--- a/src/zipfile.h
+++ b/src/zipfile.h
@@ -2,7 +2,14 @@
 
 #include "platform.h"
 #include "tuple.h"
+#if defined(__clang__)
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wnullability-extension"
+#endif
 #include <zip.h>
+#if defined(__clang__)
+#pragma clang diagnostic pop
+#endif
 
 
 namespace Jopa { // Open namespace Jopa block
diff --git a/vendor/jikespg/src/lpgparse.c b/vendor/jikespg/src/lpgparse.c
index 7e19d4a4..082e1fd9 100644
--- a/vendor/jikespg/src/lpgparse.c
+++ b/vendor/jikespg/src/lpgparse.c
@@ -392,7 +392,8 @@ static void options(void)
 
     while (parm[i] != '\0')     /* Repeat until parm line is exhausted */
     {
-        strcpy(parm, parm + i);       /* Remove garbage in front */
+        /* Use memmove because source and destination overlap. */
+        memmove(parm, parm + i, strlen(parm + i) + 1);       /* Remove garbage in front */
 
         i = 0;
 
@@ -442,7 +443,8 @@ static void options(void)
             {                                  /* prefix?         */
                 flag = FALSE;
                 len = len-2;
-                strcpy(token, token + 2);  /* get rid of "NO" prefix */
+                /* Overlapping copy; memmove keeps it defined. */
+                memmove(token, token + 2, strlen(token + 2) + 1);  /* get rid of "NO" prefix */
             }
             else
                 flag = TRUE;