diff --git a/bazel/wrlib/BUILD.bazel b/bazel/wrlib/BUILD.bazel
index ae593512..d11b3ba0 100644
--- a/bazel/wrlib/BUILD.bazel
+++ b/bazel/wrlib/BUILD.bazel
@@ -1,9 +1,26 @@
 load("@rules_rust//rust:defs.bzl", "rust_library")
 
+rust_library(
+    name = "error_code",
+    srcs = ["error_code.rs"],
+    edition = "2021",
+    visibility = ["//visibility:public"],
+)
+
+cc_test(
+    name = "error_code_cc_test",
+    srcs = ["error_code_test.c"],
+    deps = [":error_code"],
+)
+
 rust_library(
     name = "wrlib_rs",
     srcs = ["wrlib.rs"],
-    deps = [":wrlib"],
+    deps = [
+        ":ppm",
+        ":rimage",
+        ":wrlib",
+    ],
     visibility = ["//visibility:public"],
     edition = "2021",
 )
diff --git a/bazel/wrlib/error_code.rs b/bazel/wrlib/error_code.rs
new file mode 100644
index 00000000..4c073408
--- /dev/null
+++ b/bazel/wrlib/error_code.rs
@@ -0,0 +1,107 @@
+use std::{
+    os::raw::{c_char, c_int},
+    sync::RwLock,
+};
+
+static ERROR_STATUS: RwLock<ErrorCode> = RwLock::new(ErrorCode::None);
+
+#[repr(i16)]
+#[derive(Debug, Clone, Copy)]
+pub enum ErrorCode {
+    /// No known error status.
+    None = 0,
+
+    /// Can't open file.
+    Open = 1,
+
+    /// Error reading from file.
+    Read = 2,
+
+    /// Error writing to file.
+    Write = 3,
+
+    /// Out of memory.
+    NoMemory = 4,
+
+    /// Out of color cells.
+    NoColor = 5,
+
+    /// Image file is corrupted or invalid.
+    BadImageFile = 6,
+
+    /// Image file format is unknown.
+    BadFormat = 7,
+
+    /// No such image index in file.
+    BadIndex = 8,
+
+    /// Invalid visual ID requested for context.
+    BadVisualId = 16,
+
+    /// Failed to create std colormap.
+    StdCmapFail = 17,
+
+    /// Internal X11 error.
+    XError = 127,
+
+    /// Should not happen.
+    Internal = 128,
+}
+
+/// Sets the global error status in a thread-safe way. Panics if the error
+/// status lock has been poisoned.
+pub fn wraster_set_error_code(code: ErrorCode) {
+    *ERROR_STATUS.write().unwrap() = code;
+}
+
+/// Sets the global error status to a literal `value`. Panics if `value` does
+/// not correspond to a valid error value.
+#[no_mangle]
+pub unsafe extern "C" fn wraster_report_error_code(value: c_int) {
+    let value = match value {
+        0 => ErrorCode::None,
+        1 => ErrorCode::Open,
+        2 => ErrorCode::Read,
+        3 => ErrorCode::Write,
+        4 => ErrorCode::NoMemory,
+        5 => ErrorCode::NoColor,
+        6 => ErrorCode::BadImageFile,
+        7 => ErrorCode::BadFormat,
+        8 => ErrorCode::BadIndex,
+        16 => ErrorCode::BadVisualId,
+        17 => ErrorCode::StdCmapFail,
+        127 => ErrorCode::XError,
+        128 => ErrorCode::Internal,
+        _ => panic!("unknown error code: {}", value),
+    };
+    *ERROR_STATUS.write().unwrap() = value;
+}
+
+/// Returns the current error status. Panics if the error status lock has been
+/// poisoned.
+#[no_mangle]
+pub extern "C" fn wraster_current_error_code() -> i16 {
+    *ERROR_STATUS.read().unwrap() as i16
+}
+
+/// Returns a human-readable description of the current error status. Panics if
+/// the error status lock has been poisoned.
+#[no_mangle]
+pub extern "C" fn wraster_current_error_message() -> *const c_char {
+    // TODO: i18n of these messages.
+    match *ERROR_STATUS.read().unwrap() {
+        ErrorCode::None => c"no error".as_ptr(),
+        ErrorCode::Open => c"could not open file".as_ptr(),
+        ErrorCode::Read => c"error reading from file".as_ptr(),
+        ErrorCode::Write => c"error writing to file".as_ptr(),
+        ErrorCode::NoMemory => c"out of memory".as_ptr(),
+        ErrorCode::NoColor => c"out of color cells".as_ptr(),
+        ErrorCode::BadImageFile => c"invalid or corrupted image file".as_ptr(),
+        ErrorCode::BadFormat => c"image format is not supported".as_ptr(),
+        ErrorCode::BadIndex => c"file does not contain requested image index".as_ptr(),
+        ErrorCode::BadVisualId => c"request for an invalid Visual ID".as_ptr(),
+        ErrorCode::StdCmapFail => c"failed to create X standard colormap".as_ptr(),
+        ErrorCode::XError => c"internal X error".as_ptr(),
+        ErrorCode::Internal => c"internal error".as_ptr(),
+    }
+}
diff --git a/bazel/wrlib/error_code_test.c b/bazel/wrlib/error_code_test.c
new file mode 100644
index 00000000..2010e6f0
--- /dev/null
+++ b/bazel/wrlib/error_code_test.c
@@ -0,0 +1,40 @@
+#include <assert.h>
+#include <string.h>
+
+/* error codes */
+#define RERR_NONE		0
+#define RERR_OPEN	 	1      /* cant open file */
+#define RERR_READ		2      /* error reading from file */
+#define RERR_WRITE		3      /* error writing to file */
+#define RERR_NOMEMORY		4      /* out of memory */
+#define RERR_NOCOLOR		5      /* out of color cells */
+#define RERR_BADIMAGEFILE	6      /* image file is corrupted or invalid */
+#define RERR_BADFORMAT		7      /* image file format is unknown */
+#define RERR_BADINDEX		8      /* no such image index in file */
+
+#define RERR_BADVISUALID	16     /* invalid visual ID requested for context */
+#define RERR_STDCMAPFAIL	17     /* failed to created std colormap */
+
+#define RERR_XERROR		127    /* internal X error */
+#define RERR_INTERNAL		128    /* should not happen */
+
+void wraster_report_error_code(int value);
+
+const char* wraster_current_error_message();
+
+int wraster_current_error_code();
+
+int main(int argc, char** argv) {
+  assert(wraster_current_error_code() == RERR_NONE);
+  assert(strcmp(wraster_current_error_message(), "no error") == 0);
+
+  wraster_report_error_code(RERR_WRITE);
+
+  assert(wraster_current_error_code() == RERR_WRITE);
+  assert(strcmp(wraster_current_error_message(), "error writing to file") == 0);
+ 
+  wraster_report_error_code(RERR_OPEN);
+
+  assert(wraster_current_error_code() == RERR_OPEN);
+  assert(strcmp(wraster_current_error_message(), "could not open file") == 0);
+}