diff --git a/demo.c b/demo.c
index b860ff8..a7c13f4 100644
--- a/demo.c
+++ b/demo.c
@@ -53,31 +53,33 @@ void printResults(ZoneDetectResult *results, float safezone)
     if(index) {
         printf("Safezone: %f\n", safezone);
     }
-    printf("\n\n");
+}
+
+void onError(int errZD, int errNative)
+{
+    fprintf(stderr, "ZD error: %s (0x%08X)\n", ZDGetErrorString(errZD), (unsigned)errNative);
 }
 
 int main(int argc, char *argv[])
 {
-    ZoneDetect *cd;
     if(argc != 4) {
         printf("Usage: %s dbname lat lon\n", argv[0]);
-        exit(0);
+        return 1;
     }
 
-    cd = ZDOpenDatabase(argv[1]);
-    if(!cd) {
-        printf("Init failed\n");
-        exit(0);
-    }
+    ZDSetErrorHandler(onError);
 
-    float lat = atof(argv[2]);
-    float lon = atof(argv[3]);
+    ZoneDetect *const cd = ZDOpenDatabase(argv[1]);
+    if(!cd) return 2;
+
+    const float lat = (float)atof(argv[2]);
+    const float lon = (float)atof(argv[3]);
 
     float safezone = 0;
     ZoneDetectResult *results = ZDLookup(cd, lat, lon, &safezone);
     printResults(results, safezone);
 
     ZDCloseDatabase(cd);
+
     return 0;
 }
-
diff --git a/library/zonedetect.c b/library/zonedetect.c
index f766306..aadd218 100644
--- a/library/zonedetect.c
+++ b/library/zonedetect.c
@@ -26,6 +26,8 @@
  */
 
 #include <sys/mman.h>
+#include <assert.h>
+#include <errno.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -36,6 +38,16 @@
 
 #include "zonedetect.h"
 
+enum ZDInternalError {
+    ZD_OK,
+    ZD_E_DB_OPEN,
+    ZD_E_DB_SEEK,
+    ZD_E_DB_MMAP,
+    ZD_E_DB_MUNMAP,
+    ZD_E_DB_CLOSE,
+    ZD_E_PARSE_HEADER
+};
+
 struct ZoneDetectOpaque {
     int fd;
     off_t length;
@@ -54,6 +66,12 @@ struct ZoneDetectOpaque {
     uint32_t dataOffset;
 };
 
+static void (*zdErrorHandler)(int, int);
+static void zdError(enum ZDInternalError errZD, int errNative)
+{
+    if (zdErrorHandler) zdErrorHandler((int)errZD, errNative);
+}
+
 static int32_t ZDFloatToFixedPoint(float input, float scale, unsigned int precision)
 {
     const float inputScaled = input / scale;
@@ -373,12 +391,8 @@ void ZDCloseDatabase(ZoneDetect *library)
         if(library->notice) {
             free(library->notice);
         }
-        if(library->mapping) {
-            munmap(library->mapping, (size_t)(library->length));
-        }
-        if(library->fd >= 0) {
-            close(library->fd);
-        }
+        if(library->mapping && munmap(library->mapping, (size_t)(library->length))) zdError(ZD_E_DB_MUNMAP, errno);
+        if(library->fd >= 0 && close(library->fd))                                  zdError(ZD_E_DB_CLOSE , errno);
         free(library);
     }
 }
@@ -392,22 +406,26 @@ ZoneDetect *ZDOpenDatabase(const char *path)
 
         library->fd = open(path, O_RDONLY | O_CLOEXEC);
         if(library->fd < 0) {
+            zdError(ZD_E_DB_OPEN, errno);
             goto fail;
         }
 
         library->length = lseek(library->fd, 0, SEEK_END);
         if(library->length <= 0) {
+            zdError(ZD_E_DB_SEEK, errno);
             goto fail;
         }
         lseek(library->fd, 0, SEEK_SET);
 
         library->mapping = mmap(NULL, (size_t)library->length, PROT_READ, MAP_PRIVATE | MAP_FILE, library->fd, 0);
         if(!library->mapping) {
+            zdError(ZD_E_DB_MMAP, errno);
             goto fail;
         }
 
         /* Parse the header */
         if(ZDParseHeader(library)) {
+            zdError(ZD_E_PARSE_HEADER, 0);
             goto fail;
         }
     }
@@ -604,3 +622,26 @@ const char *ZDLookupResultToString(ZDLookupResult result)
     return "Unknown";
 }
 
+#define ZD_E_COULD_NOT(msg) "could not " msg
+
+const char *ZDGetErrorString(int errZD)
+{
+    switch ((enum ZDInternalError)errZD) {
+        default: assert(0);
+        case ZD_OK                : return "";
+        case ZD_E_DB_OPEN         : return ZD_E_COULD_NOT("open database file");
+        case ZD_E_DB_SEEK         : return ZD_E_COULD_NOT("retrieve database file size");
+        case ZD_E_DB_MMAP         : return ZD_E_COULD_NOT("map database file to system memory");
+        case ZD_E_DB_MUNMAP       : return ZD_E_COULD_NOT("unmap database");
+        case ZD_E_DB_CLOSE        : return ZD_E_COULD_NOT("close database file");
+        case ZD_E_PARSE_HEADER    : return ZD_E_COULD_NOT("parse database header");
+    }
+}
+
+#undef ZD_E_COULD_NOT
+
+int ZDSetErrorHandler(void (*handler)(int, int))
+{
+    zdErrorHandler = handler;
+    return 0;
+}
diff --git a/library/zonedetect.h b/library/zonedetect.h
index 79417de..4986e93 100644
--- a/library/zonedetect.h
+++ b/library/zonedetect.h
@@ -67,6 +67,9 @@ const char *ZDGetNotice(const ZoneDetect *library);
 uint8_t     ZDGetTableType(const ZoneDetect *library);
 const char *ZDLookupResultToString(ZDLookupResult result);
 
+int         ZDSetErrorHandler(void (*handler)(int, int));
+const char *ZDGetErrorString(int error);
+
 #ifdef __cplusplus
 }
 #endif