diff --git a/pkgs/by-name/ef/efficient-compression-tool/ect-gcc-15-O3-fix.patch b/pkgs/by-name/ef/efficient-compression-tool/ect-gcc-15-O3-fix.patch
new file mode 100644
index 000000000000..f4c6221058e3
--- /dev/null
+++ b/pkgs/by-name/ef/efficient-compression-tool/ect-gcc-15-O3-fix.patch
@@ -0,0 +1,13 @@
+diff --git a/src/LzFind.c b/src/LzFind.c
+index 98d0ac6..f1bee55 100755
+--- a/src/LzFind.c
++++ b/src/LzFind.c
+@@ -229,7 +229,7 @@ static unsigned short * GetMatches2(UInt32 lenLimit, UInt32 curMatch, UInt32 pos
+     const unsigned char* _min = min;
+     unsigned cnt = 0;
+     if (_min < pb - (rle_len - len)) {_min = pb - (rle_len - len);}
+-    while (rle_pos > _min && *(uint64_t*)(rle_pos - 8) == starter_full) {rle_pos-=8; cnt+=8;}
++    while (rle_pos > _min && *(__typeof__(const uint64_t __attribute__((aligned(1))))*)(rle_pos - 8) == starter_full) {rle_pos-=8; cnt+=8;}
+     if (cnt) {
+       if (cnt + len > rle_len - 1) {cnt = rle_len - 1 - len;}
+       curMatch_rle -= cnt;
diff --git a/pkgs/by-name/ef/efficient-compression-tool/package.nix b/pkgs/by-name/ef/efficient-compression-tool/package.nix
index 10da59dc6f3b..6871e59a01f7 100644
--- a/pkgs/by-name/ef/efficient-compression-tool/package.nix
+++ b/pkgs/by-name/ef/efficient-compression-tool/package.nix
@@ -22,6 +22,11 @@ stdenv.mkDerivation (finalAttrs: {
     fetchSubmodules = true;
   };
 
+  patches = [
+    # from https://github.com/fhanau/Efficient-Compression-Tool/issues/145
+    ./ect-gcc-15-O3-fix.patch
+  ];
+
   # devendor libpng
   postPatch = ''
     substituteInPlace src/CMakeLists.txt \