diff --git a/Libraries/LibC/dlfcn.cpp b/Libraries/LibC/dlfcn.cpp
index f4437b0272..7efb88d2c1 100644
--- a/Libraries/LibC/dlfcn.cpp
+++ b/Libraries/LibC/dlfcn.cpp
@@ -6,20 +6,24 @@ extern "C" {
 int dlclose(void*)
 {
     ASSERT_NOT_REACHED();
+    return 0;
 }
 
 char* dlerror()
 {
     ASSERT_NOT_REACHED();
+    return nullptr;
 }
 
 void* dlopen(const char*, int)
 {
     ASSERT_NOT_REACHED();
+    return nullptr;
 }
 
 void* dlsym(void*, const char*)
 {
     ASSERT_NOT_REACHED();
+    return nullptr;
 }
 }
diff --git a/Libraries/LibC/malloc.cpp b/Libraries/LibC/malloc.cpp
index d5364f5161..db3fc2beeb 100644
--- a/Libraries/LibC/malloc.cpp
+++ b/Libraries/LibC/malloc.cpp
@@ -146,7 +146,7 @@ void* malloc(size_t size)
     LOCKER(malloc_lock());
 
     if (s_log_malloc)
-        dbgprintf("LibC: malloc(%u)\n", size);
+        dbgprintf("LibC: malloc(%zu)\n", size);
 
     if (!size)
         return nullptr;
@@ -190,13 +190,13 @@ void* malloc(size_t size)
     block->m_freelist = block->m_freelist->next;
     if (block->is_full()) {
 #ifdef MALLOC_DEBUG
-        dbgprintf("Block %p is now full in size class %u\n", block, good_size);
+        dbgprintf("Block %p is now full in size class %zu\n", block, good_size);
 #endif
         allocator->usable_blocks.remove(block);
         allocator->full_blocks.append(block);
     }
 #ifdef MALLOC_DEBUG
-    dbgprintf("LibC: allocated %p (chunk in block %p, size %u)\n", ptr, block, block->bytes_per_chunk());
+    dbgprintf("LibC: allocated %p (chunk in block %p, size %zu)\n", ptr, block, block->bytes_per_chunk());
 #endif
     if (s_scrub_malloc)
         memset(ptr, MALLOC_SCRUB_BYTE, block->m_size);
diff --git a/Libraries/LibC/scanf.cpp b/Libraries/LibC/scanf.cpp
index bbf86cd1b5..3f2cf97b7a 100644
--- a/Libraries/LibC/scanf.cpp
+++ b/Libraries/LibC/scanf.cpp
@@ -30,6 +30,7 @@
  */
 #include <ctype.h>
 #include <stdarg.h>
+#include <stdint.h>
 #include <stdio.h>
 #include <string.h>
 
@@ -60,7 +61,8 @@ static const char* determine_base(const char* p, int& base)
 static int _atob(unsigned long* vp, const char* p, int base)
 {
     unsigned long value, v1, v2;
-    char *q, tmp[20];
+    const char *q;
+    char tmp[20];
     int digit;
 
     if (p[0] == '0' && (p[1] == 'x' || p[1] == 'X')) {
diff --git a/Libraries/LibC/ulimit.cpp b/Libraries/LibC/ulimit.cpp
index 14e7cb8c34..33e7f4390a 100644
--- a/Libraries/LibC/ulimit.cpp
+++ b/Libraries/LibC/ulimit.cpp
@@ -8,5 +8,6 @@ long ulimit(int cmd, long newlimit)
     (void)cmd;
     (void)newlimit;
     ASSERT_NOT_REACHED();
+    return -1;
 }
 }