diff --git a/CHANGES b/CHANGES
index bca70f25e..31feb2cd9 100644
--- a/CHANGES
+++ b/CHANGES
@@ -45,6 +45,7 @@ Misc:
  - SDL: Fix 2.0.5 build on macOS under some circumstances
  - Test: Restructure test suite into multiple executables
  - Python: Integrate tests from cinema test suite
+ - Util: Don't build crc32 if the function already exists
 
 0.6.0: (2017-07-16)
 Features:
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 527dacdac..cc87c268d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -500,6 +500,14 @@ if(USE_ZLIB)
 	include_directories(AFTER ${ZLIB_INCLUDE_DIRS})
 	list(APPEND DEPENDENCY_LIB ${ZLIB_LIBRARIES})
 	set(CPACK_DEBIAN_PACKAGE_DEPENDS "${CPACK_DEBIAN_PACKAGE_DEPENDS},zlib1g")
+	set(HAVE_CRC32 ON)
+else()
+	# zlib pulls in crc32
+	check_function_exists(crc32 HAVE_CRC32)
+endif()
+
+if(HAVE_CRC32)
+	list(APPEND FUNCTION_DEFINES HAVE_CRC32)
 endif()
 
 if(WANT_PNG AND USE_ZLIB AND NOT USE_PNG)
diff --git a/include/mgba-util/crc32.h b/include/mgba-util/crc32.h
index 225998bb9..ba5e694fd 100644
--- a/include/mgba-util/crc32.h
+++ b/include/mgba-util/crc32.h
@@ -12,8 +12,13 @@ CXX_GUARD_START
 
 struct VFile;
 
+#ifndef HAVE_CRC32
+uint32_t crc32(uint32_t crc, const void* buf, size_t size);
+#else
+#include <zlib.h>
+#endif
+
 uint32_t doCrc32(const void* buf, size_t size);
-uint32_t updateCrc32(uint32_t crc, const void* buf, size_t size);
 uint32_t fileCrc32(struct VFile* file, size_t endOffset);
 
 CXX_GUARD_END
diff --git a/src/util/crc32.c b/src/util/crc32.c
index 21a4354d4..24f611111 100644
--- a/src/util/crc32.c
+++ b/src/util/crc32.c
@@ -48,6 +48,7 @@ enum {
 	BUFFER_SIZE = 1024
 };
 
+#ifndef HAVE_CRC32
 static uint32_t crc32Table[] = {
 	0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419, 0x706af48f,
 	0xe963a535, 0x9e6495a3,	0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988,
@@ -93,12 +94,14 @@ static uint32_t crc32Table[] = {
 	0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94,
 	0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d
 };
+#endif
 
 uint32_t doCrc32(const void* buf, size_t size) {
-	return updateCrc32(0, buf, size);
+	return crc32(0, buf, size);
 }
 
-uint32_t updateCrc32(uint32_t crc, const void* buf, size_t size) {
+#ifndef HAVE_CRC32
+uint32_t crc32(uint32_t crc, const void* buf, size_t size) {
 	const uint8_t* p = buf;
 	
 	crc = ~crc;
@@ -108,9 +111,10 @@ uint32_t updateCrc32(uint32_t crc, const void* buf, size_t size) {
 
 	return ~crc;
 }
+#endif
 
 uint32_t fileCrc32(struct VFile* vf, size_t endOffset) {
-	char buffer[BUFFER_SIZE];
+	uint8_t buffer[BUFFER_SIZE];
 	size_t blocksize;
 	size_t alreadyRead = 0;
 	if (vf->seek(vf, 0, SEEK_SET) < 0) {
@@ -124,7 +128,7 @@ uint32_t fileCrc32(struct VFile* vf, size_t endOffset) {
 		}
 		blocksize = vf->read(vf, buffer, toRead);
 		alreadyRead += blocksize;
-		crc = updateCrc32(crc, buffer, blocksize);
+		crc = crc32(crc, buffer, blocksize);
 		if (blocksize < toRead) {
 			return 0;
 		}
diff --git a/src/util/patch-ups.c b/src/util/patch-ups.c
index 5f24311ef..ea1d531eb 100644
--- a/src/util/patch-ups.c
+++ b/src/util/patch-ups.c
@@ -154,7 +154,7 @@ bool _BPSApplyPatch(struct Patch* patch, const void* in, size_t inSize, void* ou
 		case 0x0:
 			// SourceRead
 			memmove(&writeBuffer[writeLocation], &readBuffer[writeLocation], length);
-			outputChecksum = updateCrc32(outputChecksum, &writeBuffer[writeLocation], length);
+			outputChecksum = crc32(outputChecksum, &writeBuffer[writeLocation], length);
 			writeLocation += length;
 			break;
 		case 0x1:
@@ -162,7 +162,7 @@ bool _BPSApplyPatch(struct Patch* patch, const void* in, size_t inSize, void* ou
 			if (patch->vf->read(patch->vf, &writeBuffer[writeLocation], length) != (ssize_t) length) {
 				return false;
 			}
-			outputChecksum = updateCrc32(outputChecksum, &writeBuffer[writeLocation], length);
+			outputChecksum = crc32(outputChecksum, &writeBuffer[writeLocation], length);
 			writeLocation += length;
 			break;
 		case 0x2:
@@ -177,7 +177,7 @@ bool _BPSApplyPatch(struct Patch* patch, const void* in, size_t inSize, void* ou
 				return false;
 			}
 			memmove(&writeBuffer[writeLocation], &readBuffer[readSourceLocation], length);
-			outputChecksum = updateCrc32(outputChecksum, &writeBuffer[writeLocation], length);
+			outputChecksum = crc32(outputChecksum, &writeBuffer[writeLocation], length);
 			writeLocation += length;
 			readSourceLocation += length;
 			break;
@@ -198,7 +198,7 @@ bool _BPSApplyPatch(struct Patch* patch, const void* in, size_t inSize, void* ou
 				++writeLocation;
 				++readTargetLocation;
 			}
-			outputChecksum = updateCrc32(outputChecksum, &writeBuffer[writeLocation - length], length);
+			outputChecksum = crc32(outputChecksum, &writeBuffer[writeLocation - length], length);
 			break;
 		}
 	}