diff --git a/src/fileio.cpp b/src/fileio.cpp
index e17eaf654a..851090c071 100644
--- a/src/fileio.cpp
+++ b/src/fileio.cpp
@@ -254,7 +254,8 @@ void FioOpenFile(int slot, const char *filename, Subdirectory subdir)
 #endif /* LIMITED_FDS */
 	f = FioFOpenFile(filename, "rb", subdir);
 	if (f == NULL) usererror("Cannot open file '%s'", filename);
-	uint32 pos = ftell(f);
+	long pos = ftell(f);
+	if (pos < 0) usererror("Cannot read file '%s'", filename);
 
 	FioCloseFile(slot); // if file was opened before, close it
 	_fio.handles[slot] = f;
@@ -271,7 +272,7 @@ void FioOpenFile(int slot, const char *filename, Subdirectory subdir)
 	_fio.usage_count[slot] = 0;
 	_fio.open_handles++;
 #endif /* LIMITED_FDS */
-	FioSeekToFile(slot, pos);
+	FioSeekToFile(slot, (uint32)pos);
 }
 
 static const char * const _subdirs[] = {
diff --git a/src/newgrf_config.cpp b/src/newgrf_config.cpp
index bbd670a71c..df86850302 100644
--- a/src/newgrf_config.cpp
+++ b/src/newgrf_config.cpp
@@ -360,10 +360,10 @@ static bool CalcGRFMD5Sum(GRFConfig *config, Subdirectory subdir)
 	f = FioFOpenFile(config->filename, "rb", subdir, &size);
 	if (f == NULL) return false;
 
-	size_t start = ftell(f);
+	long start = ftell(f);
 	size = min(size, GRFGetSizeOfDataSection(f));
 
-	if (fseek(f, start, SEEK_SET) < 0) {
+	if (start < 0 || fseek(f, start, SEEK_SET) < 0) {
 		FioFCloseFile(f);
 		return false;
 	}
diff --git a/src/smallmap_gui.cpp b/src/smallmap_gui.cpp
index 8e53ade6ff..85a1236264 100644
--- a/src/smallmap_gui.cpp
+++ b/src/smallmap_gui.cpp
@@ -1418,10 +1418,12 @@ int SmallMapWindow::GetPositionOnLegend(Point pt)
 		case WID_SM_LEGEND: // Legend
 			if (this->map_type == SMT_INDUSTRY || this->map_type == SMT_LINKSTATS || this->map_type == SMT_OWNER) {
 				int click_pos = this->GetPositionOnLegend(pt);
+				if (click_pos < 0) break;
+
 				/* If industry type small map*/
 				if (this->map_type == SMT_INDUSTRY) {
 					/* If click on industries label, find right industry type and enable/disable it. */
-					if (click_pos >= 0 && click_pos < _smallmap_industry_count) {
+					if (click_pos < _smallmap_industry_count) {
 						this->SelectLegendItem(click_pos, _legend_from_industries, _smallmap_industry_count);
 					}
 				} else if (this->map_type == SMT_LINKSTATS) {