diff --git a/src/solvers/Makefile b/src/solvers/Makefile
index 6279ec7f5aa..aeabd7e28ea 100644
--- a/src/solvers/Makefile
+++ b/src/solvers/Makefile
@@ -166,6 +166,7 @@ SRC = $(BOOLEFORCE_SRC) \
       refinement/string_builtin_function.cpp \
       refinement/string_refinement.cpp \
       refinement/string_refinement_util.cpp \
+      refinement/string_constraint.cpp \
       refinement/string_constraint_generator_code_points.cpp \
       refinement/string_constraint_generator_comparison.cpp \
       refinement/string_constraint_generator_concat.cpp \
diff --git a/src/solvers/refinement/string_constraint.cpp b/src/solvers/refinement/string_constraint.cpp
new file mode 100644
index 00000000000..4312dd4b745
--- /dev/null
+++ b/src/solvers/refinement/string_constraint.cpp
@@ -0,0 +1,21 @@
+/*******************************************************************\
+
+ Module: String solver
+
+ Author: Diffblue Ltd.
+
+\*******************************************************************/
+
+#include "string_constraint.h"
+
+string_constraintt::string_constraintt(
+  symbol_exprt _univ_var,
+  exprt lower_bound,
+  exprt upper_bound,
+  exprt body)
+  : univ_var(_univ_var),
+    lower_bound(lower_bound),
+    upper_bound(upper_bound),
+    body(body)
+{
+}
diff --git a/src/solvers/refinement/string_constraint.h b/src/solvers/refinement/string_constraint.h
index 3284faa6305..ee643998dfc 100644
--- a/src/solvers/refinement/string_constraint.h
+++ b/src/solvers/refinement/string_constraint.h
@@ -71,13 +71,7 @@ class string_constraintt final
     symbol_exprt _univ_var,
     exprt lower_bound,
     exprt upper_bound,
-    exprt body)
-    : univ_var(_univ_var),
-      lower_bound(lower_bound),
-      upper_bound(upper_bound),
-      body(body)
-  {
-  }
+    exprt body);
 
   // Default bound inferior is 0
   string_constraintt(symbol_exprt univ_var, exprt upper_bound, exprt body)