diff --git a/lib/CMakeLists.txt b/lib/CMakeLists.txt
index 331798d8..d4c5978c 100644
--- a/lib/CMakeLists.txt
+++ b/lib/CMakeLists.txt
@@ -16,6 +16,7 @@ add_library(libprjxray
 	xilinx/xc7series/row.cc
 	xilinx/xc7series/frames.cc
 	xilinx/xc7series/utils.cc
+	xilinx/xc7series/ecc.cc
 )
 target_include_directories(libprjxray PUBLIC "include")
 target_link_libraries(libprjxray absl::optional absl::strings absl::span absl::time yaml-cpp)
diff --git a/lib/include/prjxray/xilinx/xc7series/ecc.h b/lib/include/prjxray/xilinx/xc7series/ecc.h
index 6abab633..40e131b3 100644
--- a/lib/include/prjxray/xilinx/xc7series/ecc.h
+++ b/lib/include/prjxray/xilinx/xc7series/ecc.h
@@ -10,37 +10,7 @@ namespace xc7series {
 // Extend the current ECC code with one data word (32 bit) at a given
 // word index in the configuration frame and return the new ECC code.
 
-uint32_t icap_ecc(uint32_t idx, uint32_t data, uint32_t ecc) {
-	uint32_t val = idx * 32;  // bit offset
-
-	if (idx > 0x25)  // avoid 0x800
-		val += 0x1360;
-	else if (idx > 0x6)  // avoid 0x400
-		val += 0x1340;
-	else  // avoid lower
-		val += 0x1320;
-
-	if (idx == 0x32)  // mask ECC
-		data &= 0xFFFFE000;
-
-	for (int i = 0; i < 32; i++) {
-		if (data & 1)
-			ecc ^= val + i;
-
-		data >>= 1;
-	}
-
-	if (idx == 0x64) {  // last index
-		uint32_t v = ecc & 0xFFF;
-		v ^= v >> 8;
-		v ^= v >> 4;
-		v ^= v >> 2;
-		v ^= v >> 1;
-		ecc ^= (v & 1) << 12;  // parity
-	}
-
-	return ecc;
-}
+uint32_t icap_ecc(uint32_t idx, uint32_t data, uint32_t ecc);
 
 }  // namespace xc7series
 }  // namespace xilinx
diff --git a/lib/xilinx/xc7series/ecc.cc b/lib/xilinx/xc7series/ecc.cc
new file mode 100644
index 00000000..7c56cb8e
--- /dev/null
+++ b/lib/xilinx/xc7series/ecc.cc
@@ -0,0 +1,41 @@
+#include <prjxray/xilinx/xc7series/ecc.h>
+
+namespace prjxray {
+namespace xilinx {
+namespace xc7series {
+
+uint32_t icap_ecc(uint32_t idx, uint32_t data, uint32_t ecc) {
+	uint32_t val = idx * 32;  // bit offset
+
+	if (idx > 0x25)  // avoid 0x800
+		val += 0x1360;
+	else if (idx > 0x6)  // avoid 0x400
+		val += 0x1340;
+	else  // avoid lower
+		val += 0x1320;
+
+	if (idx == 0x32)  // mask ECC
+		data &= 0xFFFFE000;
+
+	for (int i = 0; i < 32; i++) {
+		if (data & 1)
+			ecc ^= val + i;
+
+		data >>= 1;
+	}
+
+	if (idx == 0x64) {  // last index
+		uint32_t v = ecc & 0xFFF;
+		v ^= v >> 8;
+		v ^= v >> 4;
+		v ^= v >> 2;
+		v ^= v >> 1;
+		ecc ^= (v & 1) << 12;  // parity
+	}
+
+	return ecc;
+}
+
+}  // namespace xc7series
+}  // namespace xilinx
+}  // namespace prjxray