diff --git a/src/geom/IntersectionMatrix.cpp b/src/geom/IntersectionMatrix.cpp
index 82acfcf4ef..f7ace8a9e7 100644
--- a/src/geom/IntersectionMatrix.cpp
+++ b/src/geom/IntersectionMatrix.cpp
@@ -144,7 +144,7 @@ IntersectionMatrix::set(Location row, Location col, int dimensionValue)
 void
 IntersectionMatrix::set(const std::string& dimensionSymbols)
 {
-    auto limit = dimensionSymbols.length();
+    auto limit = std::min(dimensionSymbols.length(), static_cast<std::size_t>(9));
 
     for(std::size_t i = 0; i < limit; i++) {
         auto row = i / firstDim;
diff --git a/tests/unit/capi/GEOSRelatePatternMatchTest.cpp b/tests/unit/capi/GEOSRelatePatternMatchTest.cpp
index c5f34a40b9..b60ab1e188 100644
--- a/tests/unit/capi/GEOSRelatePatternMatchTest.cpp
+++ b/tests/unit/capi/GEOSRelatePatternMatchTest.cpp
@@ -78,5 +78,18 @@ void object::test<5>
     ensure_equals(ret, char(0));
 }
 
+// invalid DE-9IM argument
+// https://github.com/libgeos/geos/issues/1084
+template<>
+template<>
+void object::test<6>
+()
+{
+    const char* mat = "0000000000";
+    ensure_equals(strlen(mat), 10u); // not a valid DE-9IM!
+
+    GEOSRelatePatternMatch(mat,  "111111111");
+}
+
 } // namespace tut